stop defaulting to fancy output on Windows

Summary:
At some point we should do proper terminal capability detection, but
until then just disable the fancy stuff on Windows. I took a quick look
at Colorama, but that didn't seem to support the control codes we need.

Test Plan:
Ran a sync on Windows. Confirmed the default output is quiet and that
errors don't have junk around them.

Reviewers: sean

Reviewed By: sean

Differential Revision: https://phabricator.buildinspace.com/D131