[puppet][tripleo][neutron][ops] Removing support for Nuage "core" plugin

Hello,

As part of the clean-up effort in puppet-neutron, I was looking at the git repository for nuage plugin and got the observation that Nuage core plugin no longer exists and only ml2 plugin is available.

https://github.com/nuagenetworks/nuage-openstack-neutron/commit/06b5fe68630c...

Based on that observation, I've proposed some patches to deprecate/remove support for Nuage core plugin, which can be found by the following link. https://review.opendev.org/q/topic:nuage-core-plugin

Unfortunately I'm not fully familiar with the integration of neutron + Nuage. I'd appreciate it if anybody familiar with it can share any concerns here or in these patches.

Thank you, Takashi