[V8] Remove unused methods in V8Proxy
https://bugs.webkit.org/show_bug.cgi?id=93106

Reviewed by Adam Barth.

In preparation for removing V8Proxy, we can remove unused methods in V8Proxy.

No tests. No change in behavior.

* bindings/v8/V8Proxy.h:
(V8Proxy):


git-svn-id: svn://svn.chromium.org/blink/trunk@124630 bbb929c8-8fbe-4397-9dbb-9b2b20218538