Revert deprecation warning on Neutron auth.

This reverts the deprecation warning added in commit
e80cf75fc0f25f6279200f59a70fd7c6e4766b0f.

V3 supports domain + project uniqueness, which is much more usable
than ids - massively more so for deployers. The initial patch
deprecates name, when that isn't necessary or appropriate - using name
based auth is as valid as id based auth - we just need to namespace
it in V3.

For V3 operators should be able to create:

* A service domain
* A service/service project
* A service/neutron user

to replace the prior

* service tenant
* neutron user

structure without switching to ids.

Closes-Bug: #1290540
Change-Id: I51837b0dc1bc352c0bf315e383951486b3cac034
Merge "Revert deprecation warning on Neutron auth."