Remove feature flag from upgrade link in user menu

This feature flag :upgrade_link_in_user_menu_a was introduced in 13.11
converted from :upgrade_link_in_user_menu_a_experiment_percentage

Changelog: added

changelogs/unreleased/remove_feature_flag_upgrade_link_in_user_menu_a.yml

+---
+title: Remove feature flag from upgrade link in user menu
+merge_request: 61057
+author:
+type: added

config/feature_flags/development/upgrade_link_in_user_menu_a.yml

----
-name: upgrade_link_in_user_menu_a
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/56591
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/300824
-milestone: '13.11'
-type: development
-group: group::expansion
-default_enabled: true

ee/app/helpers/ee/users_helper.rb

@@ -23,7 +23,6 @@ module EE
     def show_upgrade_link?(user)
       return unless user
       return unless ::Gitlab.com?
-      return unless ::Feature.enabled?(:upgrade_link_in_user_menu_a, default_enabled: :yaml)
 
       Rails.cache.fetch(['users', user.id, 'show_upgrade_link?'], expires_in: 10.minutes) do
         user.owns_upgradeable_namespace?