remove unneeded function from the crypto stream interface

stream.go

@@ -30,11 +30,6 @@ type streamI interface {
 	IsFlowControlBlocked() bool
 }
 
-type cryptoStream interface {
-	streamI
-	SetReadOffset(protocol.ByteCount)
-}
-
 // A Stream assembles the data from StreamFrames and provides a super-convenient Read-Interface
 //
 // Read() and Write() may be called concurrently, but multiple calls to Read() or Write() individually must be synchronized manually.
@@ -481,11 +476,3 @@ func (s *stream) IsFlowControlBlocked() bool {
 func (s *stream) GetWindowUpdate() protocol.ByteCount {
 	return s.flowController.GetWindowUpdate()
 }
-
-// SetReadOffset sets the read offset.
-// It is only needed for the crypto stream.
-// It must not be called concurrently with any other stream methods, especially Read and Write.
-func (s *stream) SetReadOffset(offset protocol.ByteCount) {
-	s.readOffset = offset
-	s.frameQueue.readPosition = offset
-}