### What it does
Checks for usage of `Box<T>` where an unboxed `T` would
work fine.

### Why is this bad?
This is an unnecessary allocation, and bad for
performance. It is only necessary to allocate if you wish to move the box
into something.

### Example
```
fn foo(x: Box<u32>) {}
```

Use instead:
```
fn foo(x: u32) {}
```