binding: Removes unused code in templates/attributes.cpp.

Faking {{cpp_class}} and {{c8_class}} doesn't make sense.
Probably it made sense before the introduction of virtual
ScriptWrappable::wrap().

Checking the existence of window->document() doesn't seem
making sense to me, and CQ tests seem passing without the
check.

BUG=

Review-Url: https://codereview.chromium.org/2268433002
Cr-Commit-Position: refs/heads/master@{#413375}
static void perWorldBindingsTestInterfaceEmptyMethodMethodCallback(const v8::FunctionCallbackInfo<v8::Value>& info)
{
    TestInterfaceNodeV8Internal::perWorldBindingsTestInterfaceEmptyMethodMethod(info);
}

static void perWorldBindingsTestInterfaceEmptyMethodMethodCallback(const v8::FunctionCallbackInfo<v8::Value>& info)
{
    TestInterfaceNodeV8Internal::perWorldBindingsTestInterfaceEmptyMethodMethod(info);
}
