Add dependency descriptor stream tracker for svc codecs (#1788)

* Add dependency descriptor stream tracker for svc codecs

* Solve comments

pkg/sfu/buffer/buffer.go

@@ -94,9 +94,8 @@ type Buffer struct {
 	logger logger.Logger
 
 	// dependency descriptor
-	ddExt             uint8
-	ddParser          *DependencyDescriptorParser
-	maxLayerChangedCB func(int32, int32)
+	ddExt    uint8
+	ddParser *DependencyDescriptorParser
 
 	paused              bool
 	frameRateCalculator [DefaultMaxLayerSpatial + 1]FrameRateCalculator
@@ -175,9 +174,6 @@ func (b *Buffer) Bind(params webrtc.RTPParameters, codec webrtc.RTPCodecCapabili
 				b.frameRateCalculator[i] = frc.GetFrameRateCalculatorForSpatial(int32(i))
 			}
 			b.ddParser = NewDependencyDescriptorParser(b.ddExt, b.logger, func(spatial, temporal int32) {
-				if b.maxLayerChangedCB != nil {
-					b.maxLayerChangedCB(spatial, temporal)
-				}
 				frc.SetMaxLayer(spatial, temporal)
 			})
 
@@ -779,12 +775,6 @@ func (b *Buffer) GetAudioLevel() (float64, bool) {
 	return b.audioLevel.GetLevel()
 }
 
-// DD-TODO : now we rely on stream tracker for layer change, dependency still
-// work for that too. Do we keep it unchanged or use both methods?
-func (b *Buffer) OnMaxLayerChanged(fn func(int32, int32)) {
-	b.maxLayerChangedCB = fn
-}
-
 func (b *Buffer) OnFpsChanged(f func()) {
 	b.Lock()
 	b.onFpsChanged = f