- removed redundant call to S_StopAllChannels()

It's the first thing that S_ClearSoundData() does anyway

src/d_main.cpp

@@ -2914,7 +2914,6 @@ void D_Cleanup()
 
 	// Music and sound should be stopped first
 	S_StopMusic(true);
-	S_StopAllChannels ();
 	S_ClearSoundData();
 	S_UnloadReverbDef();
 	G_ClearMapinfo();