[V8] Remove Event::dataTransferAttrGetterCustom() and Event::valueAttrSetterCustom()
https://bugs.webkit.org/show_bug.cgi?id=110666

Reviewed by Adam Barth.

Event::dataTransferAttrGetterCustom() is not used
(i.e. the custom method is not registered to V8).
Event::valueAttrSetterCustom() is declared but not
implemented. We can remove them.

No tests. No change in behavior.

* bindings/scripts/CodeGeneratorV8.pm:
(GenerateHeaderCustomCall):
* bindings/v8/custom/V8EventCustom.cpp:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144142 268f45cc-cd09-0410-ab3c-d52691b4dbfc