Revert to use Mounter method to check existence

What does this MR do?

Revert a change on gitlab-ce that we never get into gitlab-ee due to spec failures and a lack of a proper solution. So we want to keep both repos in the same codebase about this.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #22768 (closed)