deps: remove extra field from v8::HeapStatistics

Remove the `_malloced_memory` field from the `HeapStatistics`
class to achieve full ABI compatibility with V8 5.0.

Ref: https://github.com/nodejs/node/pull/7016
PR-URL: https://github.com/nodejs/node/pull/7526
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

deps/v8/include/v8.h

@@ -5211,7 +5211,6 @@ class V8_EXPORT HeapStatistics {
   size_t total_available_size() { return total_available_size_; }
   size_t used_heap_size() { return used_heap_size_; }
   size_t heap_size_limit() { return heap_size_limit_; }
-  size_t malloced_memory() { return malloced_memory_; }
   size_t does_zap_garbage() { return does_zap_garbage_; }
 
  private:
@@ -5222,7 +5221,6 @@ class V8_EXPORT HeapStatistics {
   size_t used_heap_size_;
   size_t heap_size_limit_;
   bool does_zap_garbage_;
-  size_t malloced_memory_;
 
   friend class V8;
   friend class Isolate;

deps/v8/src/api.cc

@@ -5544,8 +5544,7 @@ HeapStatistics::HeapStatistics()
       total_available_size_(0),
       used_heap_size_(0),
       heap_size_limit_(0),
-      does_zap_garbage_(0),
-      malloced_memory_(0) {}
+      does_zap_garbage_(0) {}
 
 HeapSpaceStatistics::HeapSpaceStatistics(): space_name_(0),
                                             space_size_(0),
@@ -7446,8 +7445,6 @@ void Isolate::GetHeapStatistics(HeapStatistics* heap_statistics) {
   heap_statistics->total_available_size_ = heap->Available();
   heap_statistics->used_heap_size_ = heap->SizeOfObjects();
   heap_statistics->heap_size_limit_ = heap->MaxReserved();
-  heap_statistics->malloced_memory_ =
-      isolate->allocator()->GetCurrentMemoryUsage();
   heap_statistics->does_zap_garbage_ = heap->ShouldZapGarbage();
 }