Remove custom FormData.append() bindings code.

Source/core/html/FormData.idl

Index: Source/core/html/FormData.idl
diff --git a/Source/core/html/FormData.idl b/Source/core/html/FormData.idl
index 560abfce3453e7ac2bfcec297bc4929237b4c339..fe146ce0708ae51b699c131ff1c3ac7667244fce 100644
--- a/Source/core/html/FormData.idl
+++ b/Source/core/html/FormData.idl
@@ -33,10 +33,7 @@
     Constructor([Default=Undefined] optional HTMLFormElement form),
     ImplementedAs=DOMFormData
 ] interface FormData {
-    // void append(DOMString name, DOMString value);
-    // void append(DOMString name, Blob value, optional DOMString filename);
-    [Custom] void append([Default=Undefined] optional DOMString name,
-                         [Default=Undefined] optional DOMString value,
-                         [Default=Undefined] optional DOMString filename);
+    void append(DOMString name, Blob value, optional DOMString filename);
+    void append(DOMString name, DOMString value);
 };