Small TAP tests cleanup for Windows and unused modules

Seeing msys in TAP tests mentioned in a thread [1] tonight reminded me about
two related (well, one of them) patches I had sitting around, so rather than
forgetting again here are some small cleanups.

0001 attempts to streamline how we detect Windows in the TAP tests (after that
there is a single msys check left that I'm not sure about, but [1] seems to
imply it could go); 0002 removes some unused module includes which either were
used at some point in the past or likely came from copy/paste.

--
Daniel Gustafsson        https://vmware.com/

[1] https://postgr.es/m/0ba775a2-8aa0-0d56-d780-69427cf6f33d@dunslane.net