test-removeemptydirs: adjust to Windows behavior for the `histedit` case
Windows stay in the "same" directory and the warning message is not applicable.
This make `tests/test-removeemptydirs.t` pass on Windows.
Differential Revision: https://phab.mercurial-scm.org/D11055
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL