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

update: no longer on top of #7959 and #7838.
>> +    def _eval_real_number_relation(cls, lhs, rhs):
> 
> why we need this additional method?

Its only used by the old `_eval_sides` (now called
`_eval_simplify_helper`).

Instead, I could define different methods for _eval_simplify() for
`Equality` and `_Inequality` and then drop this.

I figured my current way is more in the spirit of the current code.
But its all internal stuff anyway.  Do you have a preference?