UpdateSongPositions

It is useful to have Player SongPositions update off of ScreenGameplay
for use with things like ArrowEffects.

ScreenGameplay, ScreenHowToPlay, and ScreenEdit stop GameSoundManager
from running GameState:UpdateSongPosition and do it themselves, so this
has no impact on the screen classes that cared about, and thus updated,
player SongPositions.

src/ScreenGameplay.cpp

@@ -1468,7 +1468,7 @@ void ScreenGameplay::UpdateSongPosition( float fDeltaTime )
 	RageTimer tm;
 	const float fSeconds = m_pSoundMusic->GetPositionSeconds( NULL, &tm );
 	const float fAdjust = SOUND->GetFrameTimingAdjustment( fDeltaTime );
-	GAMESTATE->UpdateSongPosition( fSeconds+fAdjust, GAMESTATE->m_pCurSong->m_SongTiming, tm+fAdjust, true );
+	GAMESTATE->UpdateSongPosition( fSeconds+fAdjust, GAMESTATE->m_pCurSong->m_SongTiming, tm+fAdjust );
 }
 
 void ScreenGameplay::BeginScreen()