Bug 1666347 - Delete assorted dead code after removal of vendored `psutil` r=firefox-build-system-reviewers,rstewart

Most of the deletions here come from bug 1481612, the `--with-windows-wheel` option to `mach vendor python`, which according to that commit message "is very single-purpose: it's intended to let us vendor an unpacked
wheel for psutil on Windows". Since vendoring `psutil` is something we're no longer doing, we can safely just delete that added code.

Differential Revision: https://phabricator.services.mozilla.com/D90919