remove dead code

writeReplace check occurs before writeObject is called, so the HashSet.writeReplace via its proxy does the correct thing

previous comment was factually incorrect "references to this class are ever handed out to client code" - they are
"HashTrieSet serialization takes care of the situation" - no it doesnt

So these comment are probably a relic or a prior implementation

Author: mkeskells

library/src/scala/collection/immutable/HashSet.scala

@@ -488,21 +488,6 @@ object HashSet extends ImmutableSetFactory[HashSet] {
     override def iterator: Iterator[A] = ks.iterator
     override def foreach[U](f: A => U): Unit = ks.foreach(f)
 
-    private def writeObject(out: java.io.ObjectOutputStream) {
-      // this cannot work - reading things in might produce different
-      // hash codes and remove the collision. however this is never called
-      // because no references to this class are ever handed out to client code
-      // and HashTrieSet serialization takes care of the situation
-      sys.error("cannot serialize an immutable.HashSet where all items have the same 32-bit hash code")
-      //out.writeObject(kvs)
-    }
-
-    private def readObject(in: java.io.ObjectInputStream) {
-      sys.error("cannot deserialize an immutable.HashSet where all items have the same 32-bit hash code")
-      //kvs = in.readObject().asInstanceOf[ListSet[A]]
-      //hash = computeHash(kvs.)
-    }
-
   }
 
   /**