Core: Move the titlebar / statusbar abstraction to DolphinWX

The concept of a "title bar" / "status bar" shouldn't be a core concept,
so remove the Host_UpdateStatusBar function, and move the code handles
whether to update the status bar or titlebar into DolphinWX.

Source/Core/DolphinWX/Frame.h

@@ -126,6 +126,7 @@ public:
 	void UpdateWiiMenuChoice(wxMenuItem *WiiMenuItem=nullptr);
 	void PopulateSavedPerspectives();
 	static void ConnectWiimote(int wm_idx, bool connect);
+	void UpdateTitle(const std::string &str);
 
 	const CGameListCtrl *GetGameListCtrl() const;