osd/PG: fix cleanup of pgmeta-like objects on PG deletion

osd/PG: fix cleanup of pgmeta-like objects on PG deletion

If an object has an empty 'name' field, it "looks" like a pgmeta object,
and the PG cleanup code was skipping it.  However, we were letting these
objects get created.

Fix by only skipping *our* pgmeta object.  If there are other pgmeta-like
objects in the PG collection, clean them up.

Fixes: https://tracker.ceph.com/issues/38724
Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit a0f48db5cbfc48761eeac0daa259fecbaa573969)

# Conflicts:
#	src/osd/PG.cc
- location of this code is do_delete_work in master, _delete_some in n