Remove unused comettype parameter.

Author: mkelley

astroquery/mpc/core.py

@@ -765,7 +765,6 @@ def _args_to_ephemeris_payload(self, **kwargs):
     @class_or_instance
     def get_observations_async(self, targetid, *,
                                id_type=None,
-                               comettype=None,
                                get_mpcformat=False,
                                get_raw_response=False,
                                get_query_payload=False,