Remove unnecessary scalar definitions

`DateTimeUtc` and `Url` are provided by juniper and chrono/url with
  their respective (default) features.
  No need to define them manually. (I've skimmed the docs and code)

noise.graphql

@@ -6,14 +6,6 @@ type Query {
     users: [User!]!
 }
 
-# Hopefully provided by juniper and chrono
-scalar DateTimeUtc
-# else it's probably DateTime
-# scalar DateTime
-
-# Provided by juniper and url
-scalar Url
-
 type User {
     id: ID!
     userName: String!