Make some manifold checks in MappingQGeneric dimension independent.

Make some manifold checks in MappingQGeneric dimension independent.

As of db5ea0f52db we support get_manifold on 1D manifolds, so we can remove the
overload workaround here for 1D. This changes the behavior of this function
slightly: we now correctly calculate all_manifold_ids_are_equal = false if the
cell manifold, in 1D, does not equal one of the face (vertex) manifolds.

Note that in 2D lines are faces, so we still check all lines.