[notodiff] Clean up shape diff methods
[notodiff] Clean up shape diff methods

These were confusing me, so I tried to make them more clear. Should
be a no-op change.

googlefonts/nototools,dougfelt/nototools,googlefonts/nototools,dougfelt/nototools,googlei18n/nototools,anthrotype/nototools,anthrotype/nototools,moyogo/nototools,googlefonts/nototools,moyogo/nototools,googlei18n/nototools,googlei18n/nototools,googlefonts/nototools,googlefonts/nototools,anthrotype/nototools,moyogo/nototools,dougfelt/nototools