Remove redundant description_html field from Release Rest API

This commit removes the redundant description_html field
from the Release Rest API.
The feature is still behind `remove_description_html_in_release_api`
feature flag.

changelogs/unreleased/enable-remove_description_html_in_release_api-by-default.yml

+---
+title: Remove description_html field from Release Rest API
+merge_request: 61327
+author:
+type: removed

config/feature_flags/development/remove_description_html_in_release_api.yml

@@ -5,4 +5,4 @@ rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/329188
 milestone: '13.12'
 type: development
 group: group::release
-default_enabled: false
+default_enabled: true

doc/api/releases/index.md

@@ -10,6 +10,7 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 > - Using this API you can manipulate GitLab [Release](../../user/project/releases/index.md) entries.
 > - For manipulating links as a release asset, see [Release Links API](links.md).
 > - Release Evidences were [introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/26019) in GitLab 12.5.
+> - `description_html` field was [removed](https://gitlab.com/gitlab-org/gitlab/-/issues/299447) in GitLab 13.12.
 
 ## List Releases
 
@@ -39,7 +40,6 @@ Example response:
       "tag_name":"v0.2",
       "description":"## CHANGELOG\r\n\r\n- Escape label and milestone titles to prevent XSS in GFM autocomplete. !2740\r\n- Prevent private snippets from being embeddable.\r\n- Add subresources removal to member destroy service.",
       "name":"Awesome app v0.2 beta",
-      "description_html":"\u003ch2 dir=\"auto\"\u003e\n\u003ca id=\"user-content-changelog\" class=\"anchor\" href=\"#changelog\" aria-hidden=\"true\"\u003e\u003c/a\u003eCHANGELOG\u003c/h2\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eEscape label and milestone titles to prevent XSS in GFM autocomplete. !2740\u003c/li\u003e\n\u003cli\u003ePrevent private snippets from being embeddable.\u003c/li\u003e\n\u003cli\u003eAdd subresources removal to member destroy service.\u003c/li\u003e\n\u003c/ul\u003e",
       "created_at":"2019-01-03T01:56:19.539Z",
       "released_at":"2019-01-03T01:56:19.539Z",
       "author":{
@@ -154,7 +154,6 @@ Example response:
       "tag_name":"v0.1",
       "description":"## CHANGELOG\r\n\r\n-Remove limit of 100 when searching repository code. !8671\r\n- Show error message when attempting to reopen an MR and there is an open MR for the same branch. !16447 (Akos Gyimesi)\r\n- Fix a bug where internal email pattern wasn't respected. !22516",
       "name":"Awesome app v0.1 alpha",
-      "description_html":"\u003ch2 dir=\"auto\"\u003e\n\u003ca id=\"user-content-changelog\" class=\"anchor\" href=\"#changelog\" aria-hidden=\"true\"\u003e\u003c/a\u003eCHANGELOG\u003c/h2\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eRemove limit of 100 when searching repository code. !8671\u003c/li\u003e\n\u003cli\u003eShow error message when attempting to reopen an MR and there is an open MR for the same branch. !16447 (Akos Gyimesi)\u003c/li\u003e\n\u003cli\u003eFix a bug where internal email pattern wasn't respected. !22516\u003c/li\u003e\n\u003c/ul\u003e",
       "created_at":"2019-01-03T01:55:18.203Z",
       "released_at":"2019-01-03T01:55:18.203Z",
       "author":{
@@ -243,7 +242,6 @@ Example response:
    "tag_name":"v0.1",
    "description":"## CHANGELOG\r\n\r\n- Remove limit of 100 when searching repository code. !8671\r\n- Show error message when attempting to reopen an MR and there is an open MR for the same branch. !16447 (Akos Gyimesi)\r\n- Fix a bug where internal email pattern wasn't respected. !22516",
    "name":"Awesome app v0.1 alpha",
-   "description_html":"\u003ch2 dir=\"auto\"\u003e\n\u003ca id=\"user-content-changelog\" class=\"anchor\" href=\"#changelog\" aria-hidden=\"true\"\u003e\u003c/a\u003eCHANGELOG\u003c/h2\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eRemove limit of 100 when searching repository code. !8671\u003c/li\u003e\n\u003cli\u003eShow error message when attempting to reopen an MR and there is an open MR for the same branch. !16447 (Akos Gyimesi)\u003c/li\u003e\n\u003cli\u003eFix a bug where internal email pattern wasn't respected. !22516\u003c/li\u003e\n\u003c/ul\u003e",
    "created_at":"2019-01-03T01:55:18.203Z",
    "released_at":"2019-01-03T01:55:18.203Z",
    "author":{
@@ -386,7 +384,6 @@ Example response:
    "tag_name":"v0.3",
    "description":"Super nice release",
    "name":"New release",
-   "description_html":"\u003cp dir=\"auto\"\u003eSuper nice release\u003c/p\u003e",
    "created_at":"2019-01-03T02:22:45.118Z",
    "released_at":"2019-01-03T02:22:45.118Z",
    "author":{
@@ -552,7 +549,6 @@ Example response:
    "tag_name":"v0.1",
    "description":"## CHANGELOG\r\n\r\n- Remove limit of 100 when searching repository code. !8671\r\n- Show error message when attempting to reopen an MR and there is an open MR for the same branch. !16447 (Akos Gyimesi)\r\n- Fix a bug where internal email pattern wasn't respected. !22516",
    "name":"new name",
-   "description_html":"\u003ch2 dir=\"auto\"\u003e\n\u003ca id=\"user-content-changelog\" class=\"anchor\" href=\"#changelog\" aria-hidden=\"true\"\u003e\u003c/a\u003eCHANGELOG\u003c/h2\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eRemove limit of 100 when searching repository code. !8671\u003c/li\u003e\n\u003cli\u003eShow error message when attempting to reopen an MR and there is an open MR for the same branch. !16447 (Akos Gyimesi)\u003c/li\u003e\n\u003cli\u003eFix a bug where internal email pattern wasn't respected. !22516\u003c/li\u003e\n\u003c/ul\u003e",
    "created_at":"2019-01-03T01:55:18.203Z",
    "released_at":"2019-01-03T01:55:18.203Z",
    "author":{
@@ -655,7 +651,6 @@ Example response:
    "tag_name":"v0.1",
    "description":"## CHANGELOG\r\n\r\n- Remove limit of 100 when searching repository code. !8671\r\n- Show error message when attempting to reopen an MR and there is an open MR for the same branch. !16447 (Akos Gyimesi)\r\n- Fix a bug where internal email pattern wasn't respected. !22516",
    "name":"new name",
-   "description_html":"\u003ch2 dir=\"auto\"\u003e\n\u003ca id=\"user-content-changelog\" class=\"anchor\" href=\"#changelog\" aria-hidden=\"true\"\u003e\u003c/a\u003eCHANGELOG\u003c/h2\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eRemove limit of 100 when searching repository code. !8671\u003c/li\u003e\n\u003cli\u003eShow error message when attempting to reopen an MR and there is an open MR for the same branch. !16447 (Akos Gyimesi)\u003c/li\u003e\n\u003cli\u003eFix a bug where internal email pattern wasn't respected. !22516\u003c/li\u003e\n\u003c/ul\u003e",
    "created_at":"2019-01-03T01:55:18.203Z",
    "released_at":"2019-01-03T01:55:18.203Z",
    "author":{