drm: Don't prune modes loudly when a connector is disconnected

drm_helper_probe_single_connector_modes() is responsible for pruning the
previously detected modes on a disconnected connector. We don't really
need to log, again, the full list of modes that used to be valid when
connected.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>