8335607: Serial: Remove unused collection_attempt_is_safe

Reviewed-by: tschatzl

src/hotspot/share/gc/serial/defNewGeneration.cpp

@@ -834,17 +834,6 @@ void DefNewGeneration::reset_scratch() {
   }
 }
 
-bool DefNewGeneration::collection_attempt_is_safe() {
-  if (!to()->is_empty()) {
-    log_trace(gc)(":: to is not empty ::");
-    return false;
-  }
-  if (_old_gen == nullptr) {
-    _old_gen = SerialHeap::heap()->old_gen();
-  }
-  return _old_gen->promotion_attempt_is_safe(used());
-}
-
 void DefNewGeneration::gc_epilogue(bool full) {
   assert(!GCLocker::is_active(), "We should not be executing here");
   // update the generation and space performance counters

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

@@ -228,13 +228,6 @@ class DefNewGeneration: public Generation {
   // GC support
   void compute_new_size();
 
-  // Returns true if the collection is likely to be safely
-  // completed. Even if this method returns true, a collection
-  // may not be guaranteed to succeed, and the system should be
-  // able to safely unwind and recover from that failure, albeit
-  // at some additional cost.
-  bool collection_attempt_is_safe();
-
   bool collect(bool clear_all_soft_refs);
 
   HeapWord* expand_and_allocate(size_t size, bool is_tlab);