tests/helper-runtests.sh

hgmanpage: stop using raw-unicode strings

These don't exist in Python 3, and this ends up looking a little more
explicit to Martijn and me anyway.

#
# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL