fix duplicated arrow when extracting extractors from case statements with body on next line

Fixes the following issue (copied from https://github.com/scala-ide/scala-ide/pull/686):

```scala
class foo {
  def m(ar: AnyRef) =
    ar match {
    case /*1*/A(z) if (z == 2)/*1*/ =>
      5
    case /*2*/A(z)/*2*/ =>
      z
  }

  // extractor for selection 1
  // extra ') =>' in the generated code
  object ext1 {
    def unapply(x: AnyRef) = x match {
      case A(z) if z == 2) => => Some(z)
      case _ => None
    }
  }

  // extractor for selection 1
  // extra '=>' in the generated code
  object ext2 {
    def unapply(x: AnyRef) = x match {
      case A(z) => => Some(z)
      case _ => None
    }
  }
}
```