Remove remaining traces of the Allocations Gem

What does this MR do?

In MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15834 we removed use of the data produced by the Allocations Gem. However, we never removed the code that just enables tracking of allocations. In this commit we remove all remaining traces of this Gem.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Conform by the code review guidelines
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• End-to-end tests pass (package-and-qa manual pipeline job)