tests/test-gendoc-zh_TW.t

tests: stabilize test-persistent-nodemap.t on Windows

Several issues here:

  - Hooks can't invoke shell scripts on Windows, so use `sh` to launch
  - `dd` in MSYS only recognizes `status=noxfer`
  - The `PATH` updating triggered a massive slowdown, but is no longer needed

I have no idea why, but removing the `PATH` update substantially increased the
speed of the test.  It was running finishing at ~4:30 with `--debug` and ~14:50
without it, but now completes in ~2:20 on my Windows laptop.

Differential Revision: https://phab.mercurial-scm.org/D10636

#require docutils gettext

  $ $TESTDIR/check-gendoc zh_TW
  checking for parse errors