[neutron] Removing neutron-interconnection out of stadium

Hi neutrinos,

As we discussed during the Shanghai PTG I just proposed changes to move neutron-interconnection project out of stadium to "x/" namespace. So it will not be official neutron project anymore after those changes. Patches for that are in [1] and [2]

I also proposed to remove neutron-interconnection api-ref from neutron-lib. Patch is here [3]. Please review it :)

[1] https://review.opendev.org/#/c/694478/ [2] https://review.opendev.org/#/c/694480/ [3] https://review.opendev.org/#/c/694466/