Move language detection to mandatory

Closes https://gitlab.com/gitlab-org/gitaly/issues/732
Closes https://gitlab.com/gitlab-org/gitaly/issues/360

spec/lib/gitlab/git/repository_spec.rb

@@ -1688,7 +1688,6 @@ describe Gitlab::Git::Repository, seed_helper: true do
   end
 
   describe '#languages' do
-    shared_examples 'languages' do
     it 'returns exactly the expected results' do
       languages = repository.languages('4b4918a572fa86f9771e5ba40fbd48e1eb03e2c6')
       expected_languages = [
@@ -1719,13 +1718,6 @@ describe Gitlab::Git::Repository, seed_helper: true do
     end
   end
 
-    it_behaves_like 'languages'
-
-    context 'with rugged', :skip_gitaly_mock do
-      it_behaves_like 'languages'
-    end
-  end
-
   describe '#license_short_name' do
     shared_examples 'acquiring the Licensee license key' do
       subject { repository.license_short_name }