Duplication of groups in convert UFO2 to UFO3 kerning sample implementation

[jenskutilek]

I wonder if it's intended that the UFO2 to UFO3 kerning conversion sample implementation adds the upgraded kerning group names to the existing groups instead of removing the old groups from the dict. It seems to generate a lot of unnecessary data in groups.plist.

[madig]

Is it maybe to keep the data there for tools that use it?

[typesupply]

Is it maybe to keep the data there for tools that use it?

I think that was more or less my idea. Since any group could be used as a kerning group in <= UFO2, I didn't want to assume that the group no longer served any purpose. In practice, however, this is very confusing. I think the algorithm should get a retainConverted (or something like that) option with the default being False.

@jenskutilek I'm sorry for not commenting on this earlier!