Remove feature flag definition for feature_flags_related_issues

This is a licensed feature and does not use a feature flag check

config/initializers/0_inject_feature_flags.rb

@@ -14,7 +14,6 @@ if Gitlab.ee? && Gitlab.dev_or_test_env?
   # being unique to licensed names. These feature flags should be reworked to
   # be "development" with explicit check
   IGNORED_FEATURE_FLAGS = %i[
-    feature_flags_related_issues
     group_wikis
     swimlanes
     minimal_access_role

ee/config/feature_flags/licensed/feature_flags_related_issues.yml

----
-name: feature_flags_related_issues
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/42023
-rollout_issue_url: 
-group: group::progressive delivery
-type: licensed
-default_enabled: true