### What it does
Checks for unit (`()`) expressions that can be removed.

### Why is this bad?
Such expressions add no value, but can make the code
less readable. Depending on formatting they can make a `break` or `return`
statement look like a function call.

### Example
```
fn return_unit() -> () {
    ()
}
```
is equivalent to
```
fn return_unit() {}
```