Remove music.niceplay() when returning from credits6

I'm... not sure why this was here? It's absolutely not needed.

I'm guessing maybe at one point during development, there might have
been wanted a special song to be played during the credits, or no song
at all (although the function being niceplay() instead of play() seems
to support the first possibility) - but there's no need for this to be
here.

desktop_version/src/Input.cpp

@@ -1121,7 +1121,6 @@ static void menuactionpress(void)
             music.playef(11);
             game.returnmenu();
             map.nexttowercolour();
-            music.niceplay(6);
             break;
         }
         break;