CONTRIBUTING

inno: stop shipping pywin32

Ancient versions of Mercurial relied on pywin32 and I suspect
that's why we have this dependency.

We also ship the "keyring" package, which has a dependency
on "pywin32-ctypes" (providing the "win32ctypes" package).
This is a stripped down version of pywin32 that doesn't have
as many dependencies.

Since we don't have a dependency on pywin32 and since pywin32
is a bit annoying to package, let's get rid of it.

With this change, py2exe no longers picks up DLL dependencies
on various UCRT DLLs (because we no longer have a .pyd file
beloning to pywin32 which was pulling them in). So, we were
able to remove code in support of the UCRT DLLs.

.. bc::

   The Windows Inno installers no longer ship the pywin32 package.

   This package was being bundled for historical reasons. Mercurial
   stopped using pywin32 several years ago and the disappearance
   of this package should not have any meaningful impact.

Differential Revision: https://phab.mercurial-scm.org/D6067

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