haskell-process-suggest-remove-import leaves blank line rather than completely remove it

Current implementation of `haskell-suggest-remove-import` just clears line contents but do not removes it when user answers `y`. I propose to remove entire line, e.g.

``` hs
import A
import D -- ^ this import is redundant
import B

-- current behavior
import A

import B

-- proposed
import A
import B
```