Hurray more snapshot blockers!

…s-fix, r=Jarcho

Fix false positive in `redundant_type_annotations` lint

This PR changes the `redundant_type_annotations` lint to allow slice type annotations (i.e., `&[u8]`) for byte string literals. It will still consider _array_ type annotations (i.e., `&[u8; 4]`) as redundant. The reasoning behind this is that the type of byte string literals is by default a reference to an array, but, by using a type annotation, you can force it to be a slice. For example:
```rust
let a: &[u8; 4] = b"test";
let b: &[u8] = b"test";
```

Now, the type annotation for `a` will still be linted (as it is still redundant), but the type annotation for `b` will not.

Fixes rust-lang#12212.

changelog: [`redundant_type_annotations`]: Fix false positive with byte string literals