Make 'git fsck' mandatory

What does this MR do?

Make git fsck over Gitaly Mandatory. The feature isn't used and already sends false positives in the original implementation so we'll just go ahead a migrate it completely to Gitaly.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

gitaly#769 (closed)