RFC: exclude tests and rubi from wheel

[eagleoflqj]

As we are planning to move to pytest, it may make sense to exclude sympy.test and all test files from binary wheel, as they provide no value to end users and contributes to wheel size.
Also, since rubi is broken, it shouldn't be included either.

[oscarbenjamin]

I agree on both counts.

For the tests I suggest putting them into a separate pypi project so that someone can do pip install sympy-tests. Also since #24291 proposes to add a sympy[tests] packaging extra the sympy-tests package could be added as a dependency of the extra.

For rubi it should just be developed outside of the sympy repo as a separate package at least until it works. For now I suggest just to delete rubi. It will still be there in the git history if anyone wants to extract it to a separate package.

[oscarbenjamin]

It will still be there in the git history if anyone wants to extract it to a separate package.

Although if it is straight-forward to just extract it to a separate repo in the symp organisation then that would be better.