SurfaceFlinger: set transaction flag internally for refresh rate overlay

Do not call setTransactionFlags from RefreshRateOverlay as this may
cause IdleTimer to reset. Instead just set the internal transation
state of flinger.

Test: scroll within calendar app and observe systraces
Bug: 130759239
Change-Id: I74dad1e7e9c9b28bbd2d6dec8a949028fe6052ca