Equality: less automatic simplification and fix 'Eq(p, 0)' for p positive

update: no longer on top of #7959 and #7838.
True, although I'm not sure its much worse than the `.isequal(0)` bit which suffers from same (consider `simplify(Lt(x + I, x + I + 2, evaluate=False))` now dif is a real number)

Actually `Lt(x + I, x + I + 2)` is True which might be an issue, I filed #8288.