From PR https://github.com/ManageIQ/manageiq/pull/12160:
The MiqAeServiceManageIQ_Providers_Openstack_NetworkManager_NetworkPort service model defined an association 'cloud_subnets' that was also defined in its superclass MiqAeServiceNetworkPort, so this appeared twice in its list of associations. The class MiqAeServiceNetworkPort defined an association 'cloud_subnet' that was not defined in the NetworkPort AR, so this gave a NoMethodError when accessed.
This PR removes the two erroneous lines from the service model definitions
Verified in 188.8.131.52. cloud_subnet is not defined as expected and cloud_subnets works.