8331004: Serial: Remove unused GenClosure

Reviewed-by: gli, tschatzl

Author: albertnetymk

src/hotspot/share/gc/serial/serialHeap.hpp

@@ -236,15 +236,6 @@ class SerialHeap : public CollectedHeap {
 
   void print_heap_change(const PreGenGCValues& pre_gc_values) const;
 
-  // The functions below are helper functions that a subclass of
-  // "CollectedHeap" can use in the implementation of its virtual
-  // functions.
-
-  class GenClosure : public StackObj {
-   public:
-    virtual void do_generation(Generation* gen) = 0;
-  };
-
   // Return "true" if all generations have reached the
   // maximal committed limit that they can reach, without a garbage
   // collection.