Spourious unused renamed import warning

## Compiler version

3.3.3, 3.4.0, 

## Minimized code

```Scala
//> using options -Wunused:all

def test(list: List[Int]): Int =
  import list.{head => first}
  first
```

## Output

```scala
4 |  import list.{head => first}
  |               ^^^^^^^^^^^^^
  |               unused import
```

## Expectation
Should not warn
