Remove grid_lon/lat from lon/lat standard names (#120)

Author: aulemahal

cf_xarray/accessor.py

@@ -75,8 +75,8 @@
             "ocean_sigma_z_coordinate",
             "ocean_double_sigma_coordinate",
         ),
-        "latitude": ("latitude", "grid_latitude"),
-        "longitude": ("longitude", "grid_longitude"),
+        "latitude": ("latitude",),
+        "longitude": ("longitude",),
     },
     "_CoordinateAxisType": {
         "T": ("Time",),