fix(thunder): remove duplicate _configure_launcher that dropped the external-launch guard (#2324)

Co-authored-by: Bhimraj Yadav <[email protected]>

extensions/thunder/strategies/thunder_ddp.py

@@ -111,11 +111,6 @@ class ThunderDDPStrategy(ParallelStrategy):
     def process_group_backend(self) -> str | None:
         return self._process_group_backend
 
-    @override
-    def _configure_launcher(self) -> None:
-        assert self.cluster_environment is not None
-        self._launcher = _SubprocessScriptLauncher(self.cluster_environment, self.num_processes, self.num_nodes)
-
     @override
     def setup_environment(self) -> None:
         super().setup_environment()