Cleanup dependencies for nova-base

The python-nova package now pulls the required dependency on
python-oslo-policy:

036149e93f/openstack-nova.spec (L389)

TrivialFix

Change-Id: I472f600710cb743ef6ede01e722a79b1451cf295

docker/nova/nova-base/Dockerfile.j2

@@ -4,14 +4,10 @@ MAINTAINER {{ maintainer }}
 {% if install_type == 'binary' %}
     {% if base_distro in ['centos', 'fedora', 'oraclelinux', 'rhel'] %}
 
-# TODO(mandre) remove python-oslo-policy once RDO package is fixed
-# https://github.com/openstack-packages/nova/blob/rpm-master/openstack-nova.spec
-# https://review.gerrithub.io/#/c/255435/
 RUN yum -y install \
         openstack-nova-common \
         python-keystoneclient \
         python-cinderclient \
-        python-oslo-policy \
         bridge-utils \
     && yum clean all