Warnings on unnecessary indexes

[jackfischer]

A developer on our team recently introduced the following, which obviously has the doubly-unnecessary explicit .user index. This seems like an obvious situation to emit a warning.

  CREATE TYPE default::TourConfig {
      CREATE REQUIRED LINK user: default::User;
      CREATE CONSTRAINT std::exclusive ON (.user);
      CREATE INDEX ON (.user);
      CREATE REQUIRED PROPERTY seenTourIds: array<std::str> {
          SET default := (<array<std::str>>[]);
      };
  };