wix: remove pywin32
This dependency was for ancient Mercurial versions. We recently
removed it from the Inno Setup installers. So let's remove it
from the WiX installers as well.
.. bc::
The Windows MSI installers no longer include the pywin32 Python
package.
Differential Revision: https://phab.mercurial-scm.org/D6100
#require docutils gettext
$ $TESTDIR/check-gendoc sv
checking for parse errors