Add automatically applicable suggestion to should_assert_eq lint

[killercup]

Found by running rustfix on https://github.com/space-wizards/bsdiff-rs. Hopefully not that hard assuming the lint already has a way to parse the expression as x == y.

warning: use `assert_eq` for better reporting
  --> tests/test.rs:25:5
   |
25 |     assert!(&expected == cursor.get_ref());
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(should_assert_eq)] on by default
   = help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#should_assert_eq
   = note: this error originates in a macro outside of the current crate

[killercup]

No longer necessary, lint deprecated because of rust-lang/rfcs#2011