This will make neutron-lib gate use dependency versions that are sanity
checked by jobs in openstack/requirements gate.
Since the library is itself in upper-constraints.txt file, we should
remove its entry from the constraints file before applying it, otherwise
pip will fail due to version conflict between what's in the current
library repo and what's in constraints file.
Change-Id: I6a708e7b618f2f2da9c9210a19e4d4e4ac370462
b5454ede0e