Should not delete wildcard imports

[mernst]

The tool deletes wildcard imports without leaving anything in their place, thus leading to uncompilable code.

Consider this code:

import java.util.*;

class UseList {
  List l;
}

which is transformed to this:

class UseList {
  List l;
}

[cushon]

Thanks, that's a bad bug in the unused import pass.

(Note that the style guide does not allow wildcard imports, which is probably why it didn't get caught sooner.)