Fix data race: Do not modify the message after calling next()

The message handler invoked by next, might do processing in a different
go routine, modifying the message options causes a data race. After
the message is handled, it is not reused, so the modification is not
necessary.

net/blockwise/blockwise.go

@@ -392,9 +392,6 @@ func (b *BlockWise[C]) handleReceivedMessage(w *responsewriter.ResponseWriter[C]
 		maxSZX = fitSZX(r, message.Block2, maxSZX)
 		block, errG := r.GetOptionUint32(message.Block2)
 		next(w, r)
-		if errG == nil {
-			r.Remove(message.Block2)
-		}
 		if w.Message().Code() == codes.Content && errG == nil {
 			startSendingMessageBlock = block
 		}