E0254 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/E0254.rs

E0254 needs a span_label, updating it from:

error[E0254]: an extern crate named `collections` has already been imported in this module
  --> src/test/compile-fail/E0254.rs:19:5
   |
11 | extern crate collections;
   | ------------------------- previous import of `collections` here
...
19 | use foo::collections; //~ ERROR E0254
   |     ^^^^^^^^^^^^^^^^

To:

error[E0254]: an extern crate named `collections` has already been imported in this module
  --> src/test/compile-fail/E0254.rs:19:5
   |
11 | extern crate collections;
   | ------------------------- previous import of `collections` here
...
19 | use foo::collections; //~ ERROR E0254
   |     ^^^^^^^^^^^^^^^^ already imported

[creativcoder]

I'd like to work on this.

[sophiajt]

@creativcoder - Looks like @lukehinds has already taken this one. There are some other free ones on the list if you're interested.