Incorporate knowledge of disjoint markers into simplification

[charliermarsh]

There are some markers that we "know" cannot be true at the same time, despite the fact that it's not encoded in the grammar or schema at all.

For example, this is never true: platform_system == 'Linux' and sys_platform == 'darwin'.

If we encode knowledge about the markers that we "know" are disjoint, we can omit more forks, wheels, etc.

[charliermarsh]

\cc @ibraheemdev