subset: remove assert to handle HVAR direct mapping
subset: remove assert to handle HVAR direct mapping

It looks like this was (at least partially) implemented in
https://github.com/fonttools/fonttools/commit/f01c86ca9be788ac16c86a60dc70241aa98287ea

Should fix https://github.com/fonttools/fonttools/issues/1237

I'm still not sure about that "File a bug." when AdvWidthMap is None,
but either LsbMap or RsbMap are not None..

And we still need to add tests for this though.

googlefonts/fonttools,fonttools/fonttools