Revert "Two ideas to make it easier to express facts in the assumptions"

This reverts commit 8599878e61a3ed96459d815d04dade8a06c9bcd0.

I don't really like either of these ideas. I'd rather express things as
Implies(Q.zero(x) & Q.positive(y), Q.zero(x**y)) than
Q.zero(Q.zero**Q.positive).

Conflicts:
	sympy/assumptions/assume.py