Update query simplification

Rails 5 didn't like the arel usage, see:
https://gitlab.com/gitlab-org/gitlab-ce/issues/49873#note_92040225

This change makes that right, but also makes the query nicer. I'm not
sure anymore why it didn't work before, however there were issues with
it that have been resolved.

app/services/projects/detect_repository_languages_service.rb

@@ -13,10 +13,9 @@ module Projects
 
         detection.updates.each do |update|
           RepositoryLanguage
-            .arel_table.update_manager
             .where(project_id: project.id)
             .where(programming_language_id: update[:programming_language_id])
-            .set(share: update[:share])
+            .update_all(share: update[:share])
         end
 
         Gitlab::Database.bulk_insert(