af6020320d
The following is a weird pattern for a file within `rustc_middle`:
```
use rustc_middle::aaa;
use crate::bbb;
```
More sensible and standard would be this:
```
use crate::{aaa, bbb};
```
I.e. we generally prefer using `crate::` to using a crate's own name.
(Exceptions are things like in macros where `crate::` doesn't work
because the macro is used in multiple crates.)
This commit fixes a bunch of these weird qualifiers.