Don't constantly commit CA transactions when scrubbing video

Closes #488

Tusker/Screens/Gallery/VideoControlsViewController.swift

@@ -256,10 +256,8 @@ private class VideoScrubbingControl: UIControl {
     
     private func updateFillLayerMask() {
         // I don't know where this animation is coming from
-        CATransaction.begin()
-        CATransaction.setDisableActions(true)
         fillMaskLayer.frame = CGRect(x: 0, y: 0, width: fractionComplete * bounds.width, height: 8)
-        CATransaction.commit()
+        fillMaskLayer.removeAllAnimations()
     }
     
     override func beginTracking(_ touch: UITouch, with event: UIEvent?) -> Bool {