delete: remove --cache-only option, fixes #7440

for deleting the cache only, use:

borg rdelete --cache-only

src/borg/archiver/delete_cmd.py

@@ -142,12 +142,6 @@ class DeleteMixIn:
         subparser.add_argument(
             "-s", "--stats", dest="stats", action="store_true", help="print statistics for the deleted archive"
         )
-        subparser.add_argument(
-            "--cache-only",
-            dest="cache_only",
-            action="store_true",
-            help="delete only the local cache for the given repository",
-        )
         subparser.add_argument(
             "--force",
             dest="forced",