Fix backup remove for alternate locations

Currently the API converts backup locations on network mounts to
the Supervisor's Mount representation. However, the locations stored
in the backup representations is a dictionary with the location
string as key.

Make sure to use the backup location string to validate the remove
requests. This fixes removing backups from network storage mounts.

supervisor/backups/manager.py

@@ -263,9 +263,9 @@ def remove(
         """Remove a backup."""
         targets = (
             [
-                self._get_location_name(location)
+                location_name
                 for location in locations
-                if location in backup.all_locations
+                if (location_name := self._get_location_name(location)) in backup.all_locations
             ]
             if locations
             else list(backup.all_locations.keys())