Remove unnecessary assertion about cull_distance

Remove unnecessary assertion about cull_distance, as this is
handled by the logic that follows.

compass/landice/mesh.py

@@ -369,12 +369,6 @@ def set_cell_width(self, section_name, thk, bed=None, vx=None, vy=None,
     # cell size in the final mesh. There may be a more rigorous way to set
     # that distance.
     if dist_to_edge is not None:
-        assert (cull_distance < 3. * max(high_dist, high_dist_bed)), \
-            ('cull_distance is set to be larger than 3x the max of high_dist '
-             'and high_dist_bed, which means max_spac is not being applied to '
-             'the regions of the mesh that will be culled, which means the '
-             'mesh generation is likely to be substantially slower '
-             'than necessary.  Please fix or relax this constraint.')
         mask = np.logical_and(
             thk == 0.0, dist_to_edge > (3. * cull_distance))
         logger.info('Setting cell_width in outer regions to max_spac '