rgw: RGWSI_SysObj_Cache::remove() invalidates after successful delete

rgw: RGWSI_SysObj_Cache::remove() invalidates after successful delete

invalidating the cache before the librados delete means that a racing call
to `RGWSI_SysObj_Cache::read()` may succeed and repopulate the cache. in
that case, subsequent reads will continue to return cached data even after
the librados delete succeeds

Fixes: https://tracker.ceph.com/issues/64480
Signed-off-by: Casey Bodley <cbodley@redhat.com>