Remove useless function updategraphicsmode()

Now that it does nothing due to some earlier changes, it's a useless
function that does nothing. (Well, it was already a useless function,
but those earlier changes made it clearer just exactly how useless it
is.) So remove that function and remove all its callsites.

desktop_version/src/titlerender.cpp

@@ -20,10 +20,6 @@ int tb;
 
 std::string tempstring;
 
-void updategraphicsmode()
-{
-}
-
 void titlerender()
 {