Removes sites dfw10 and dfw11 (#58)

Now that periodic clients are under control in DFW, we can remove these
additional virtual sites. They have already been out of production for some
weeks now, and also removed from siteinfo. This change will just remove the VMs
from GCP and the cluster.

mlab-oti/platform-cluster.tf

@@ -81,24 +81,6 @@ module "platform-cluster" {
       mlab3-dfw09 = {
         zone = "us-south1-a"
       },
-      mlab1-dfw10 = {
-        zone = "us-south1-c"
-      },
-      mlab2-dfw10 = {
-        zone = "us-south1-b"
-      },
-      mlab3-dfw10 = {
-        zone = "us-south1-a"
-      },
-      mlab1-dfw11 = {
-        zone = "us-south1-c"
-      },
-      mlab2-dfw11 = {
-        zone = "us-south1-b"
-      },
-      mlab3-dfw11 = {
-        zone = "us-south1-a"
-      },
       mlab1-doh01 = {
         # We cannot currently get any N2 quota in this region.
         machine_type = "e2-highcpu-4"