temp file for stat table not deleted after successful export

[RosaWagner]

I have this file HedvigLettersSerif-Regular[opsz].ttf.stat.yaml in the variablefont directory each time after export. In https://github.com/RosaWagner/HedvigLetters/commit/2cd282da2077b297b69cf16758144342ed11e32c

Also instances_ttf is not removed after successful export of (only) otf-cff fonts.

[simoncozens]

This is something which will get fixed when builder2 lands, as builder2 is more conscientious about putting temporary files in the temporary directory.

[RickyDaMa]

This can probably be closed now, no longer seeing this issue on v0.9.52