Fixes #36347 - Remove YumMetadataFile

[jturel]

I see this poor issue has been bumped from release to release and decided to give it a shot.

What are the changes introduced in this pull request?

Removes YumMetadataFile model and supporting code

Considerations taken when implementing this change?

There are some leftovers that I think are still used(?)

git grep -i metadatafile app/
app/lib/katello/util/pulpcore_content_filters.rb:      def filter_metadatafiles_by_pulp_hrefs(metadatafiles_results, _package_pulp_hrefs)
app/lib/katello/util/pulpcore_content_filters.rb:        metadatafiles_results.collect { |result| result.pulp_href }.flatten.uniq
app/services/katello/pulp3/api/yum.rb:          PulpRpmClient::ContentRepoMetadataFilesApi.new(api_client)
app/services/katello/pulp3/repository/yum.rb:        def metadatafiles(options = {})
app/services/katello/pulp3/repository/yum.rb:          metadata_file_hrefs_to_include = filter_metadatafiles_by_pulp_hrefs(
app/services/katello/pulp3/repository/yum.rb:            repo_service.metadatafiles(options)&.results, content_unit_hrefs)

What are the testing steps for this pull request?

Make sure there's a green build and ... anything else?