chore: Removes the unrealistic todo comment of visibility management

Co-authored-by: Wei Sun (Jack) <weisun@google.com>
PiperOrigin-RevId: 829041637

Author: Jacksunwei

src/google/adk/agents/callback_context.py

@@ -45,8 +45,6 @@ def __init__(
     from ..events.event_actions import EventActions
     from ..sessions.state import State
 
-    # TODO(weisun): make this public for Agent Development Kit, but private for
-    # users.
     self._event_actions = event_actions or EventActions()
     self._state = State(
         value=invocation_context.session.state,