Remove PEFT compatibility changes in config

We'll wait for the PEFT release that fixes this for good.

src/lerobot/configs/policies.py

@@ -91,12 +91,6 @@ class PreTrainedConfig(draccus.ChoiceRegistry, HubMixin, abc.ABC):
             )
             self.use_amp = False
 
-    def get(self, name, default=None):
-        return getattr(self, name, default)
-
-    def __contains__(self, name):
-        return hasattr(self, name)
-
     @property
     def type(self) -> str:
         return self.get_choice_name(self.__class__)