Removes display_outdated_line_diff feature flag

Changelog: added

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/345491

app/models/note.rb

@@ -609,7 +609,6 @@ class Note < ApplicationRecord
 
   def show_outdated_changes?
     return false unless for_merge_request?
-    return false unless Feature.enabled?(:display_outdated_line_diff, noteable.source_project, default_enabled: :yaml)
     return false unless system?
     return false unless change_position&.line_range
 

config/feature_flags/development/display_outdated_line_diff.yml

----
-name: display_outdated_line_diff
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/72597
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/345491
-milestone: '14.5'
-type: development
-group: group::code review
-default_enabled: true