fixes#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
```
Such implementations are usually mistakes and are not used in the
compiler or standard library (after this commit) so forbid them with
`min_specialization`.
