Remove all return True from pass_kincuts

Created by: Zaharid

I have an idea on how to make the cuts specification fancy and understandable, https://github.com/NNPDF/nnpdf/issues/236. There is the issue that it isn't happening any time soon. Even if I was bored and wanted to work on the fancy parser described there, there is still the problem that the rules in https://github.com/NNPDF/nnpdf/blob/566c6b27c269d04f1f98597b1fe980f541acffd6/validphys2/src/validphys/filters.py#L151 are non commutative and generally difficult to follow. It would be very helpful if we got rid of the return True statements. It is of course non trivial in that one needs to alter the rules so that they stay the same. The benefit is that if we only have return False, then we can reorder at will.