Mojo: removing support for process-group.

services/catalog/data/serialization

 {
   "name": "service:foo",
   "display_name": "Foo",
-  "process-group": "bar",
   "interface_provider_specs": {
     "service_manager:connector": {
       "provides": {
         "foo": [ "mojo::Bar", "mojo::Baz" ],
         "bar": [ "mojo::Bork" ]
       },
       "requires": {
         "service:bar": [ "a", "b" ]
       }
     }
   }
 }