refactor some uses of getPotentialRequiredSignoffs

[bhearsum]

This pattern is used often (but not exclusively) with getPotentialRequiredSignoffs. It might be possible (at some point) to refactor the function so that it returns the data without further manipulation ?

potential_required_signoffs = [
    obj for v in self.getPotentialRequiredSignoffs([row, new_row], transaction=transaction).values() for obj in v
]

Originally posted by @nthomas-mozilla in #1265