Revert "load_masters: actually assign font attributes" (#1486)

* Revert "load_masters: actually assign font attributes"

This reverts commit ef1d4cd02d1e46f5dac3914f547a6e4275cf3077, which caused a
crash in `interpolate_layout()` when `deepcopy`ing OTFs.

Amend code and tests while I work on a real fix.

3 files changed