Remove discover from test-requirements
It's only needed for python < 2.7 which is not supported
# of appearance. Changing the order has an impact on the overall integration
# process, which may cause wedges in the gate later.
coverage>=4.0 # Apache-2.0
-discover # BSD
fixtures>=3.0.0 # Apache-2.0/BSD
hacking<0.11,>=0.10.0
mock>=2.0 # BSD
