narrow: remove narrowpatch instead of narrowcopies
84092edd5c88 removed narrowpatch.py and wanted to drop narrowpatch from
__init__.py but mistakenly removed narrowcopies.
This will make buildbots green again.
Differential Revision: https://phab.mercurial-scm.org/D4837
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL