rgw/lc: stop using merge_and_store_attrs in remove_bucket_config

rgw/lc: stop using merge_and_store_attrs in remove_bucket_config

merge_and_store_attrs() is no longer able to remove xattrs. change the
sal::Bucket's attrs manually and call put_info() to write them back

Fixes: https://tracker.ceph.com/issues/71083
Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit f3cc52124c650d32be2adf3cf540167142423c42)

Conflicts:
	src/rgw/driver/rados/rgw_bucket.cc
	src/rgw/driver/rados/rgw_sal_rados.cc
	src/rgw/rgw_lc.cc
	src/rgw/rgw_lc.h
	src/rgw/rgw_op.cc
  mostly because squid doesn't have changes to remove metadata backends