font_project: move booleanOperations import inside 'remove_overalap' method
font_project: move booleanOperations import inside 'remove_overalap' method

If one passes --keep-overalap option, then booleanOperations should not be required by fontmake.

googlefonts/fontmake,googlei18n/fontmake,googlefonts/fontmake,googlei18n/fontmake