Clarify optional feature flag cleanup approach

This removes the recently-introduced Feature Flag Removal issue
template, in favor of adding an optional checkbox to the Feature
Flag Roll Out template. The intent of this change is to reduce
complexity while preserving flexibility.

.gitlab/issue_templates/Feature Flag Removal.md

-<!-- Title suggestion: [Feature flag] Remove FEATURE_FLAG_NAME -->
-
-## Feature
-
-The `:feature_name` feature flag was previously [enabled by default](URL) and should be removed.
-
-## Owners
-
-- Group: ~"group::GROUP_NAME"
-- Slack channel: `#g_GROUP_NAME`
-- DRI: USERNAME
-- PM: USERNAME
-
-**Removal**
-
-This is an __important__ phase, that should be either done in the next Milestone or as soon as possible. For the cleanup phase, please follow our documentation on how to  [clean up the feature flag](https://docs.gitlab.com/ee/development/feature_flags/controls.html#cleaning-up).
-
-- [ ] Remove `:feature_name` feature flag
-    - [ ] Remove all references to the feature flag from the codebase
-    - [ ] Remove the YAML definitions for the feature from the repository
-    - [ ] Create a Changelog Entry
-
-- [ ] Clean up the feature flag from all environments by running this chatops command in `#production` channel `/chatops run feature delete some_feature`.
-
-- [ ] Close this issue after the feature flag is removed from the codebase.
-
-/label ~"feature flag" ~"technical debt"
-/assign DRI

.gitlab/issue_templates/Feature Flag Roll Out.md

@@ -110,15 +110,15 @@ To do so, follow these steps:
       the feature can be officially announced in a release blog post.
     - [ ] `/chatops run auto_deploy status <merge-commit>`
 - [ ] Close [the feature issue](ISSUE LINK) to indicate the feature will be released in the current milestone.
+- [ ] (Optional) Close this issue and create a separate issue for scheduling the steps below to "Clean up the feature flag".
 
-**WARNING:** This approach has the downside that it makes it difficult for us to
-[clean up](https://docs.gitlab.com/ee/development/feature_flags/controls.html#cleaning-up) the flag.
+**WARNING:** This approach complicates [clean up](https://docs.gitlab.com/ee/development/feature_flags/controls.html#cleaning-up).
 For example, on-premise users could disable the feature on their GitLab instance. But when you
 remove the flag at some point, they suddenly see the feature as enabled and they can't roll it back
 to the previous behavior. To avoid this potential breaking change, use this approach only for urgent
 matters.
 
-### Release the feature
+### Clean up the feature flag
 
 After the feature has been [deemed stable](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#including-a-feature-behind-feature-flag-in-the-final-release),
 the [clean up](https://docs.gitlab.com/ee/development/feature_flags/controls.html#cleaning-up)