By tracking import use types to check whether it is scope uses or the other situations like module-relative uses, we can do more accurate redundant import checking.

fixes rust-lang#117448

For example unnecessary imports in std::prelude that can be eliminated:

```rust
use std::option::Option::Some;//~ WARNING the item `Some` is imported redundantly
use std::option::Option::None; //~ WARNING the item `None` is imported redundantly
```

Author: surechen

src/driver.rs

@@ -28,7 +28,6 @@ use std::fs::read_to_string;
 use std::ops::Deref;
 use std::path::Path;
 use std::process::exit;
-use std::string::ToString;
 
 use anstream::println;