Rewrite rugged ref updates to use gitaly RPCs

What does this MR do and why?

#336749 (closed)

Soon we will begin to use the praefect database in tests and when this happens we can no longer rely on being able to directly manipulate repositories without praefect knowing.

Ref updates are low hanging fruit that can easily be migrated to RPCs in bulk.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

ee/spec/models/repository_spec.rb

@@ -18,8 +18,7 @@
   let(:repository) { project.repository }
 
   def create_remote_branch(remote_name, branch_name, target)
-    rugged = rugged_repo(repository)
-    rugged.references.create("refs/remotes/#{remote_name}/#{branch_name}", target.id)
+    repository.write_ref("refs/remotes/#{remote_name}/#{branch_name}", target.id)
   end
 
   describe 'delegated methods' do