Selecting a song is supposed to be final.

stepmania/src/ScreenSelectMusic.cpp

@@ -912,14 +912,6 @@ void ScreenSelectMusic::MenuStart( const InputEventPlus &input )
 
 void ScreenSelectMusic::MenuBack( const InputEventPlus &input )
 {
-	if( TWO_PART_SELECTION && m_SelectionState == SelectionState_SelectingSteps )
-	{
-		m_SelectionState = SelectionState_SelectingSong;
-		// XXX: What sound should be played here?
-		SCREENMAN->PlayCancelSound();
-		return;
-	}
-
 	m_BackgroundLoader.Abort();
 
 	Cancel( SM_GoToPrevScreen );