Disable metadata creation hack in operation service tests

Praefect piggybacks on Gitalys tests for testing the various RPCs. The tests are simply run with Praefect in front of the Gitaly. This worked fine before Praefect became stricter about consistency of the operations and began requiring database records of the repositories. The database records are updated when Praefect proxies the various RPCs to the repository. Gitalys tests generally do not create the test repositories via the API but place the directly in the storage. This does not work with Praefect as Praefect won't see the changes and won't be able to update its metadata. A hack was put in place in Praefect to create the metadata in the tests when Praefect receives a request for a repository. This is not ideal as it can hide bugs in Praefect.

As all of the relevant operation service tests have now been amended to create their test repositories via the API, this commit disables the metadata creation hack for operation service tests.

Related to: #4019 (closed)