move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/telegram/dcs/prod_test.go

@@ -0,0 +1,17 @@
+package dcs
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestProd(t *testing.T) {
+	require.NotEmpty(t, Prod())
+
+	// Check copying.
+	a := Prod().Options
+	a[0].IPAddress = "10"
+	b := Prod().Options
+	require.NotEqual(t, "10", b[0].IPAddress)
+}