Remove __all__ = ... from stubs

[msullivan]

The presence of a all causes everything to not get picked up by
import *, which among other things breaks the new six.moves stubs.

[ilevkivskyi]

This looks like an OK temporary solution, but more globally I would just add the actual lists of names to __all__ in every file.

[gvanrossum]

Actually I think this is wrong. It will break legitimate code that accesses m.__all__ (for whatever reason). The root cause seems to be that if __all__ is present only names it explicitly lists are deemed public. But I think that if __all__ has type Any the assumption should be that anything defined (not imported) should be public (in stubs, non-public values needn't be included at all). We should also still assume that names starting with _ are not public. The rare stub for which this is wrong can fill in its __all__ explicitly.