Rename mojo: to service:

services/shell/tests/shutdown/shutdown_unittest_manifest.json

 {
   "manifest_version":  1,
-  "name": "mojo:shutdown_unittest",
+  "name": "service:shutdown_unittest",
   "display_name": "Shutdown Unittest",
   "capabilities": {
     "required": {
-      "mojo:shell": { "interfaces": [ "shell::mojom::ServiceManager" ] },
-      "mojo:shutdown_client": {
+      "service:shell": { "interfaces": [ "shell::mojom::ServiceManager" ] },
+      "service:shutdown_client": {
         "interfaces": [ "shell::mojom::ShutdownTestClientController" ]
       },
-      "mojo:shutdown_service": {
+      "service:shutdown_service": {
         "interfaces": [ "shell::mojom::ShutdownTestService" ]
       }
     }
   }
 }