production names are saved to .glyphs file even if same as default

Take e.g. https://gitlab.gnome.org/GNOME/cantarell-fonts, roundtrip to UFO and back.

I suppose there is a case for storing production names in the UFO, but storing them in the glyphs file again if they are the same as the default?

Reproduce the Cantarell-fonts roundtrip from the issue, converting from .glyphs to UFO and back. Inspect the resulting .glyphs file and compare production names with their defaults; done means names identical to the default are not written redundantly while necessary production names remain preserved.

Written by the indexing model from the issue text.