python3: Drop mox dependency
python3: Drop mox dependency

Drop mox dependency, it is not being used at all.

Change-Id: Ibcc971cee46dabad9c612d95593640ac139638e3
Signed-off-by: Chuck Short <753a8074f04ffd62a8fff7516e3ae689be8e35ad@canonical.com>

eayunstack/python-cinderclient,citrix-openstack-build/python-cinderclient,scottdangelo/cinderclient-api-microversions,varunarya10/python-cinderclient,swamireddy/python-cinderclient,scottdangelo/cinderclient-api-microversions,swamireddy/python-cinderclient,JioCloud/python-cinderclient,ntt-sic/python-cinderclient,metacloud/python-cinderclient,ntt-sic/python-cinderclient,JioCloud/python-cinderclient,metacloud/python-cinderclient,varunarya10/python-cinderclient,eayunstack/python-cinderclient,citrix-openstack-build/python-cinderclient