fix & doc: update selector prompt documentation and remove validation…

… checks

python/packages/autogen-agentchat/src/autogen_agentchat/teams/_group_chat/_selector_group_chat.py

@@ -259,7 +259,7 @@ class SelectorGroupChat(BaseGroupChat, Component[SelectorGroupChatConfig]):
             Without a termination condition, the group chat will run indefinitely.
         max_turns (int, optional): The maximum number of turns in the group chat before stopping. Defaults to None, meaning no limit.
         selector_prompt (str, optional): The prompt template to use for selecting the next speaker.
-            Must contain '{roles}', '{participants}', and '{history}' to be filled in.
+            Available fields: '{roles}', '{participants}', and '{history}'.
         allow_repeated_speaker (bool, optional): Whether to include the previous speaker in the list of candidates to be selected for the next turn.
             Defaults to False. The model may still select the previous speaker -- a warning will be logged if this happens.
         max_selector_attempts (int, optional): The maximum number of attempts to select a speaker using the model. Defaults to 3.
@@ -418,13 +418,6 @@ def __init__(
         # Validate the participants.
         if len(participants) < 2:
             raise ValueError("At least two participants are required for SelectorGroupChat.")
-        # Validate the selector prompt.
-        if "{roles}" not in selector_prompt:
-            raise ValueError("The selector prompt must contain '{roles}'")
-        if "{participants}" not in selector_prompt:
-            raise ValueError("The selector prompt must contain '{participants}'")
-        if "{history}" not in selector_prompt:
-            raise ValueError("The selector prompt must contain '{history}'")
         self._selector_prompt = selector_prompt
         self._model_client = model_client
         self._allow_repeated_speaker = allow_repeated_speaker