Remove cache_shared_runners_enabled FF

This change removes the cache_shared_runners_enabled feature flag.

Changelog: removed

config/feature_flags/development/cache_shared_runners_enabled.yml

----
-name: cache_shared_runners_enabled
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/68002
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/338267
-milestone: '14.2'
-type: development
-group: group::optimize
-default_enabled: true

ee/app/models/ee/namespace.rb

@@ -282,11 +282,7 @@ module EE
     end
 
     def any_project_with_shared_runners_enabled?
-      if ::Feature.enabled?(:cache_shared_runners_enabled, self, default_enabled: :yaml)
-        Rails.cache.fetch([self, :has_project_with_shared_runners_enabled], expires_in: 5.minutes) do
-          any_project_with_shared_runners_enabled_with_cte?
-        end
-      else
+      Rails.cache.fetch([self, :has_project_with_shared_runners_enabled], expires_in: 5.minutes) do
         any_project_with_shared_runners_enabled_with_cte?
       end
     end