This reverts commit a014720912.
Reason for revert: It is not needed to have network in the EXT_PARENT_RESOURCE_MAPPING as we will keep NET_OWNER rules and use
them for subnets and ports API.
Please see [1] for more detailed explanation why it's better to keep NET_OWNER rules for those policies.
[1] https://review.opendev.org/c/openstack/neutron/+/889153
Change-Id: Ia2cd6301e04ac502888ee2b8042ea8c19873a95a