drm: drop drm_get_connector_name() and drm_get_encoder_name()

No longer used or needed as the structs have a name field.

Acked-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>