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

update: no longer on top of #7959 and #7838.
> How about ...
@smichr: I updated the docstring: I put the `Eq(cos(x)**2 + sin(x)**2, 1)` example there, with a paragraph about not simplifying.   Also, left a shorter note at the relevant part of the code about not attempting simplification.