os_networks: Drop Python 2 support

Author: markgoddard

roles/os_networks/defaults/main.yml

@@ -101,9 +101,6 @@ os_networks_security_groups: []
 #   in the designated way.
 os_networks_rbac: []
 
-# Use Train upper constraints when running with Python 2, to avoid
-# incompatibility with newer OSC releases.
-#
 # Use Yoga upper constraints otherwise, to allow compatibility with python 3.10
 # https://storyboard.openstack.org/#!/story/2008577
-os_networks_upper_constraints_file: https://releases.openstack.org/constraints/upper/{% if ansible_facts.python.version.major == 2 %}train{% else %}yoga{% endif %}
+os_networks_upper_constraints_file: https://releases.openstack.org/constraints/upper/yoga