Remove the obsolete OverwriteMode optimization.

src/full-codegen.cc

Index: src/full-codegen.cc
diff --git a/src/full-codegen.cc b/src/full-codegen.cc
index 3084580ae0e8d412e32dcc2ed8b5a5f7435b0f59..e72dc7c5fdb3f832c76440affd7545bbc0035ea2 100644
--- a/src/full-codegen.cc
+++ b/src/full-codegen.cc
@@ -1052,19 +1052,15 @@ void FullCodeGenerator::VisitArithmeticExpression(BinaryOperation* expr) {
   Comment cmnt(masm_, "[ ArithmeticExpression");
   Expression* left = expr->left();
   Expression* right = expr->right();
-  OverwriteMode mode =
-      left->ResultOverwriteAllowed()
-      ? OVERWRITE_LEFT
-      : (right->ResultOverwriteAllowed() ? OVERWRITE_RIGHT : NO_OVERWRITE);
 
   VisitForStackValue(left);
   VisitForAccumulatorValue(right);
 
   SetSourcePosition(expr->position());
   if (ShouldInlineSmiCase(op)) {
-    EmitInlineSmiBinaryOp(expr, op, mode, left, right);
+    EmitInlineSmiBinaryOp(expr, op, left, right);
   } else {
-    EmitBinaryOp(expr, op, mode);
+    EmitBinaryOp(expr, op);
   }
 }