contrib: comment out the 64-bit py38 dependency installation on Windows
Not sure what is going on here, but it appears to not install py3.8 x64 in the
usual C:\hgdev directory. The x32 installer works fine. I'm assuming this is
a bug in this version of the installer, but didn't look into it too much.
Differential Revision: https://phab.mercurial-scm.org/D11274