Remove hanging `return void 0` from if alternates about javascript

[GoodForOneFare]

Note that decaf also generates similar non-returning alternates that may be cleaned up as part of this transform (or raise a separate issue if another transform is a better idea):

  _doRequest() {
    let ref;

    if ((ref = this.operation) != null) {
      ref.abort();
    } else { // DELETE THIS ELSE.
      void 0;
    }

    this.operation = $.ajax({
      url: this.url,
    });
  }

[lemonmade]

I don't understand when CoffeeScript/ decaf decides to process things into conditional blocks versus ternaries :( I think these are probably separate transforms, but we can leave it as a single issue.

[fandy]

Fixed in #91