Host: Remove outdated comment

Host_RequestFullscreen and Host_UpdateMainFrame have been removed, and
Host_RequestRenderWindowSize has been used by DolphinQt since 80699096
and by Android since e8739156.

Source/Core/DolphinQt/Host.cpp

@@ -277,10 +277,6 @@ void Host_PPCBreakpointsChanged()
                 [] { emit Host::GetInstance()->PPCBreakpointsChanged(); });
 }
 
-// We ignore these, and their purpose should be questioned individually.
-// In particular, RequestRenderWindowSize, RequestFullscreen, and
-// UpdateMainFrame should almost certainly be removed.
-
 void Host_RequestRenderWindowSize(int w, int h)
 {
   emit Host::GetInstance()->RequestRenderSize(w, h);