Drop Jira proxy setting columns

We no longer need the Jira proxy settings columns in jira_tracker_data
table as we are using the proxy settings via environment variables.
https://docs.gitlab.com/omnibus/settings/environment-variables.html#setting-custom-environment-variables.

This reverts
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/52119.

We previously ignored the columns during 13.11 with
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/57260.

changelogs/unreleased/325938-drop-jira-proxy-setting-columns.yml

+---
+title: Drop Jira proxy setting columns
+merge_request: 60123
+author:
+type: other

db/post_migrate/20210423124223_remove_proxy_settings_to_jira_tracker_data.rb

+# frozen_string_literal: true
+
+class RemoveProxySettingsToJiraTrackerData < ActiveRecord::Migration[6.0]
+  def change
+    remove_column :jira_tracker_data, :encrypted_proxy_address, :text
+    remove_column :jira_tracker_data, :encrypted_proxy_address_iv, :text
+    remove_column :jira_tracker_data, :encrypted_proxy_port, :text
+    remove_column :jira_tracker_data, :encrypted_proxy_port_iv, :text
+    remove_column :jira_tracker_data, :encrypted_proxy_username, :text
+    remove_column :jira_tracker_data, :encrypted_proxy_username_iv, :text
+    remove_column :jira_tracker_data, :encrypted_proxy_password, :text
+    remove_column :jira_tracker_data, :encrypted_proxy_password_iv, :text
+  end
+end

db/schema_migrations/20210423124223

+6b508f1a48402aa2db3862e2e31ee4ccb851f535ed59f9b949ac1bad0ff2f0e1
\ No newline at end of file

db/structure.sql

@@ -14016,14 +14016,6 @@ CREATE TABLE jira_tracker_data (
     deployment_type smallint DEFAULT 0 NOT NULL,
     vulnerabilities_issuetype text,
     vulnerabilities_enabled boolean DEFAULT false NOT NULL,
-    encrypted_proxy_address text,
-    encrypted_proxy_address_iv text,
-    encrypted_proxy_port text,
-    encrypted_proxy_port_iv text,
-    encrypted_proxy_username text,
-    encrypted_proxy_username_iv text,
-    encrypted_proxy_password text,
-    encrypted_proxy_password_iv text,
     jira_issue_transition_automatic boolean DEFAULT false NOT NULL,
     CONSTRAINT check_0bf84b76e9 CHECK ((char_length(vulnerabilities_issuetype) <= 255)),
     CONSTRAINT check_214cf6a48b CHECK ((char_length(project_key) <= 255))