cls/rgw: index cancelation still cleans up remove_objs

cls/rgw: index cancelation still cleans up remove_objs

when multipart uploads complete their final bucket index transaction,
they pass the list of part objects in 'remove_objs' for bulk removal -
the part objects, along with their bucket stats, get replaced by the
head object

but if CompleteMultipart races with another upload, the head object
write will fail with ECANCELED and the bucket index transaction gets
canceled with CLS_RGW_OP_CANCEL. these canceled uploads still need to
clean up their 'remove_objs', but cancelation was returning too early.
as a result, these bucket index entries get orphaned and leave the
bucket stats inconsistent

this commit reworks rgw_bucket_complete_op() so that CLS_RGW_OP_CANCEL
is handled the same way as OP_ADD and OP_DEL, so always runs the loop to
clean up 'remove_objs'

Fixes: https://tracker.ceph.com/issues/53199
Signed-off-by: Casey Bodley <cbodley@redhat.com>