use a single TCP outgoing buffer each client / session (#665)

this saves memory.

client_format.go

@@ -1,8 +1,6 @@
 package gortsplib
 
 import (
-	"time"
-
 	"github.com/pion/rtcp"
 	"github.com/pion/rtp"
 
@@ -71,19 +69,6 @@ func (cf *clientFormat) stop() {
 	}
 }
 
-func (cf *clientFormat) writePacketRTP(byts []byte, pkt *rtp.Packet, ntp time.Time) error {
-	cf.rtcpSender.ProcessPacket(pkt, ntp, cf.format.PTSEqualsDTS(pkt))
-
-	ok := cf.cm.c.writer.push(func() error {
-		return cf.cm.writePacketRTPInQueue(byts)
-	})
-	if !ok {
-		return liberrors.ErrClientWriteQueueFull{}
-	}
-
-	return nil
-}
-
 func (cf *clientFormat) readRTPUDP(pkt *rtp.Packet) {
 	packets, lost := cf.udpReorderer.Process(pkt)
 	if lost != 0 {