Use google_container_cluster location argument

[William Squires]

There is now a location argument, which can be either a region or zone. https://www.terraform.io/docs/providers/google/r/container_cluster.html#location

This means we can remove the workaround we have using both a regional and zonal definition using count to control which is created.

[repo-lockdown]

This project is now deprecated so we aren't accepting any further changes.