Remove `/x-ray/libraries` endpoint

Context

The /x-ray/libraries endpoint is currently used by legacy versions of the Repository X-Ray Go image which is run in an X-Ray CI job. This CI job is officially deprecated in %17.6 and will be removed in %18.0. See gitlab-org/gitlab#500146 (closed).

As part of its removal, we will no longer support this X-Ray endpoint in AIGW.

Proposal

Remove /x-ray/libraries endpoint and all related code.