Remove unused constructor BinaryOperation(Assignment* compound_assignment).

src/ast.cc

Index: src/ast.cc
diff --git a/src/ast.cc b/src/ast.cc
index 79e5f8ad7e0c329ced14a0e5bda41d04717e45a8..7c29409bcbc3f19d1062a20991449e7fa8178790 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -337,15 +337,6 @@ bool BinaryOperation::ResultOverwriteAllowed() {
 }
 
 
-BinaryOperation::BinaryOperation(Assignment* assignment) {
-  ASSERT(assignment->is_compound());
-  op_ = assignment->binary_op();
-  left_ = assignment->target();
-  right_ = assignment->value();
-  pos_ = assignment->position();
-}
-
-
 // ----------------------------------------------------------------------------
 // Inlining support