Revert "Add HINT for restartpoint race with KeepFileRestoredFromArchive()."

Revert "Add HINT for restartpoint race with KeepFileRestoredFromArchive()."

This reverts commit 8ad6c5dbbe5a, which was a commit specific to v14 and
older branches as the race condition between restartpoints and
KeepFileRestoredFromArchive() still existed.

1f95181b44c8 has worsened the situation on these two branches, causing
spurious failures in archive recovery (neither streaming nor archive
recovery) with concurrent restartpoints.  The same logic as v15 and
newer versions will be applied in some follow-up commits to close this
problem, making this HINT not necessary anymore.

Reported-by: Arun Thirupathi
Discussion: https://postgr.es/m/20250306193013[email protected]
Backpatch-through: 13