E0207 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/impl-unused-rps-in-assoc-type.rs

Error E0207 needs a span_label, updating it from:

error[E0207]: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
  --> src/test/compile-fail/impl-unused-rps-in-assoc-type.rs:21:6
   |
21 | impl<'a> Fun for Holder { //~ ERROR E0207
   |      ^^

to:

error[E0207]: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
  --> src/test/compile-fail/impl-unused-rps-in-assoc-type.rs:21:6
   |
21 | impl<'a> Fun for Holder { //~ ERROR E0207
   |      ^^ unconstrained lifetime parameter