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/tgtest/services/err.go

@@ -0,0 +1,16 @@
+package services
+
+import (
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tgerr"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tgtest"
+)
+
+var (
+	// ErrMethodNotImplemented denotes that method is not implemented.
+	ErrMethodNotImplemented error = tgerr.New(400, "INPUT_METHOD_INVALID")
+
+	// NotImplemented is a simple handler which returns ErrMethodNotImplemented.
+	NotImplemented tgtest.HandlerFunc = func(server *tgtest.Server, req *tgtest.Request) error {
+		return ErrMethodNotImplemented
+	}
+)