Remove explicit tracking of guest view frames

This is no longer required now that we have implicit exclusion
of certain frame types including guest view frames.

Rename GuestView to ExcludedView in the renderer process.

libcef/browser/chrome/chrome_context_menu_handler.cc

@@ -256,7 +256,7 @@ class CefContextMenuObserver : public RenderViewContextMenuObserver,
     // May return nullptr if the frame is destroyed while the menu is pending.
     auto* rfh = context_menu_->GetRenderFrameHost();
     if (rfh) {
-      // May return nullptr for guest views.
+      // May return nullptr for excluded views.
       frame = browser_->GetFrameForHost(rfh);
     }
     if (!frame) {