GatherMetadata: Fix recovery and deletion for resharded files

The function S3.check_file_exists had 2 modes, one for calculated shard and another for provided one. This worked well before resharding, but now that the calculated one and the recorded will be different, we had forgotten to use the one recorded on the db for existing file.

This bug made reads from backups fail for certain files.

Fix the recovery and deletion, by using the location retrieved from teh database rather than the calculated one.

Bug: T361718