Remove a bit more dead code after array spread desugaring

src/ast/ast.cc

Index: src/ast/ast.cc
diff --git a/src/ast/ast.cc b/src/ast/ast.cc
index 068b36c7438cb3430d1d90d25e2b7183f294f7b6..3307bff78958f04e31d1c1b286210f7e1c756798 100644
--- a/src/ast/ast.cc
+++ b/src/ast/ast.cc
@@ -497,10 +497,11 @@ void ObjectLiteral::BuildConstantProperties(Isolate* isolate) {
 
 
 void ArrayLiteral::BuildConstantElements(Isolate* isolate) {
+  DCHECK_LT(first_spread_index_, 0);
+
   if (!constant_elements_.is_null()) return;
 
-  int constants_length =
-      first_spread_index_ >= 0 ? first_spread_index_ : values()->length();
+  int constants_length = values()->length();
 
   // Allocate a fixed array to hold all the object literals.
   Handle<JSArray> array = isolate->factory()->NewJSArray(