Move services/shell to services/service_manager

services/service_manager/tests/shell/shell_unittest_manifest.json

 {
   "manifest_version":  1,
   "name": "service:shell_unittest",
   "display_name": "Shell Unittest",
   "capabilities": {
     "provided": {
       "shell_unittest:create_instance_test": [
         "shell::test::mojom::CreateInstanceTest"
       ]
     },
     "required": {
       "service:shell": [ "shell:service_manager" ],
       "exe:shell_unittest_driver": [ "shell_unittest:driver" ]
     }
   }
 }