Remove set_user_last_activity feature flag

app/controllers/concerns/record_user_last_activity.rb

@@ -17,7 +17,6 @@ module RecordUserLastActivity
 
   def set_user_last_activity
     return unless request.get?
-    return unless Feature.enabled?(:set_user_last_activity, default_enabled: true)
     return if Gitlab::Database.read_only?
 
     if current_user && current_user.last_activity_on != Date.today

changelogs/unreleased/214382-remove-set_user_last_activity-feature-flag.yml

+---
+title: Remove set_user_last_activity feature flag.
+merge_request: 31795
+author: Gilang Gumilar
+type: removed