remove TLS post-handshake message reassembly logic (#4073)

Go 1.21.1 was released, which fixed the bug that made this workaround
necessary.

crypto_stream_test.go

@@ -1,7 +1,6 @@
 package quic
 
 import (
-	"crypto/rand"
 	"fmt"
 
 	"github.com/quic-go/quic-go/internal/protocol"
@@ -16,7 +15,7 @@ var _ = Describe("Crypto Stream", func() {
 	var str cryptoStream
 
 	BeforeEach(func() {
-		str = newCryptoStream(false)
+		str = newCryptoStream()
 	})
 
 	Context("handling incoming data", func() {
@@ -138,23 +137,4 @@ var _ = Describe("Crypto Stream", func() {
 			Expect(f.Data).To(Equal([]byte("bar")))
 		})
 	})
-
-	It("reassembles data", func() {
-		str = newCryptoStream(true)
-		data := make([]byte, 1337)
-		l := len(data) - 4
-		data[1] = uint8(l >> 16)
-		data[2] = uint8(l >> 8)
-		data[3] = uint8(l)
-		rand.Read(data[4:])
-
-		for i, b := range data {
-			Expect(str.GetCryptoData()).To(BeEmpty())
-			Expect(str.HandleCryptoFrame(&wire.CryptoFrame{
-				Offset: protocol.ByteCount(i),
-				Data:   []byte{b},
-			})).To(Succeed())
-		}
-		Expect(str.GetCryptoData()).To(Equal(data))
-	})
 })