E0223 needs to be updated to new format

[sophiajt]

From:

Error E0223 needs a span_label, updated title, and a note, changing it from:

error[E0223]: ambiguous associated type; specify the type using the syntax `<Type as MyTrait>::X`
  --> src/test/compile-fail/E0223.rs:14:14
   |
14 |     let foo: MyTrait::X; //~ ERROR E0223
   |              ^^^^^^^^^^

To:

error[E0223]: ambiguous associated type
  --> src/test/compile-fail/E0223.rs:14:14
   |
14 |     let foo: MyTrait::X; //~ ERROR E0223
   |              ^^^^^^^^^^ ambiguous associated type
   |
   = note: specify the type using the syntax `<Type as MyTrait>::X`

[KiChjang]

Test case in src/test/compile-fail/associated-types-in-ambiguous-context.rs