Sphinx was cargo culted into our install environment as part of
emulating TortoiseHG's behavior.
THG seems to install Sphinx in order to generate THG specific
We don't appear to need Sphinx or any of its dependencies in
the official WiX installers. So remove it.
This shaves ~1MB off the size of the MSI installers.
The Windows MSI installers no longer include the Python sphinx package and its various dependencies.