Revert "riotctrl_ctrl: one more indirection to get native"

This reverts commit 5e0c9b4bff.

dist/pythonlibs/riotctrl_ctrl/native.py

@@ -27,6 +27,5 @@ class NativeRIOTCtrl(riotctrl.ctrl.RIOTCtrl):
     def start_term(self, *args, **kwargs):
         super().start_term(*args, **kwargs)
         for child in psutil.Process(pid=self._term_pid()).children():
-            for grandchild in child.children():
-                if self._set_debug_adapter_id(grandchild):
+            if self._set_debug_adapter_id(child):
                 break

dist/pythonlibs/riotctrl_ctrl/requirements.txt

@@ -1,3 +1,2 @@
 psutil
-pyserial
 riotctrl