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/rpc/external_test.go

@@ -0,0 +1,16 @@
+package rpc
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNopDrop(t *testing.T) {
+	require.NoError(t, NopDrop(Request{}))
+}
+
+func TestNopSend(t *testing.T) {
+	require.NoError(t, NopSend(context.TODO(), 0, 0, nil))
+}