Unset GODEBUG - WHich means that Go 1.13 is now required for TLS 1.3

We could keep setting GODEBUG for compatibility with older versions, but
people complain that it prints debug warnings.

dnscrypt-proxy/main.go

@@ -28,7 +28,6 @@ type App struct {
 
 func main() {
 	dlog.Init("dnscrypt-proxy", dlog.SeverityNotice, "DAEMON")
-	os.Setenv("GODEBUG", os.Getenv("GODEBUG")+",tls13=1")
 
 	seed := make([]byte, 8)
 	crypto_rand.Read(seed)