Remove the obsolete OverwriteMode optimization.

src/code-stubs-hydrogen.cc

Index: src/code-stubs-hydrogen.cc
diff --git a/src/code-stubs-hydrogen.cc b/src/code-stubs-hydrogen.cc
index d955e9e91b0a9339cf20634d9cacf2c2b51a4fce..bccce299bddcd80a161b8771b7cccc7e51871642 100644
--- a/src/code-stubs-hydrogen.cc
+++ b/src/code-stubs-hydrogen.cc
@@ -1230,21 +1230,6 @@ HValue* CodeStubGraphBuilder<BinaryOpICStub>::BuildCodeInitializedStub() {
     result = EnforceNumberType(result, result_type);
   }
 
-  // Reuse the double box of one of the operands if we are allowed to (i.e.
-  // chained binops).
-  if (state.CanReuseDoubleBox()) {
-    HValue* operand = (state.mode() == OVERWRITE_LEFT) ? left : right;
-    IfBuilder if_heap_number(this);
-    if_heap_number.If<HHasInstanceTypeAndBranch>(operand, HEAP_NUMBER_TYPE);
-    if_heap_number.Then();
-    Add<HStoreNamedField>(operand, HObjectAccess::ForHeapNumberValue(), result);
-    Push(operand);
-    if_heap_number.Else();
-    Push(result);
-    if_heap_number.End();
-    result = Pop();
-  }
-
   return result;
 }