Revert "simplify Mul._eval_is_even"

This reverts commit 1b436d045107f610b51065e03eff0dbdf92e76c5.

This "simplification" produces loop, because Add._eval_is_odd
call in turn is_even property on Add's arguments.

fixes #8050
Merge pull request #8052 from skirpichev/8050-fix

Revert "simplify Mul._eval_is_even"