remove setting of the TLS 1.3 GODEBUG flag

p2p/security/tls/transport.go

@@ -5,7 +5,6 @@ import (
 	"crypto/tls"
 	"errors"
 	"net"
-	"os"
 	"sync"
 
 	ci "github.com/libp2p/go-libp2p-core/crypto"
@@ -13,12 +12,6 @@ import (
 	"github.com/libp2p/go-libp2p-core/sec"
 )
 
-// TLS 1.3 is opt-in in Go 1.12
-// Activate it by setting the tls13 GODEBUG flag.
-func init() {
-	os.Setenv("GODEBUG", os.Getenv("GODEBUG")+",tls13=1")
-}
-
 // ID is the protocol ID (used when negotiating with multistream)
 const ID = "/tls/1.0.0"