Summary:
As suggested in #802. By not persisting the _xy_grid buffer, we can allow (in some cases) a model with one image_size to be loaded from a saved model which was trained at a different resolution.
Also avoid persisting _frequencies in HarmonicEmbedding for similar reasons.
BC-break: This will cause load_state_dict, in strict mode, to complain if you try to load an old model with the new code.
Reviewed By: patricklabatut
Differential Revision: D30349234
fbshipit-source-id: d6061d1e51c9f79a78d61a9f732c9a5dfadbbb47