Remove unused import and clean up type hints in EventListener

src/crewai/utilities/events/event_listener.py

@@ -1,8 +1,7 @@
 from io import StringIO
-from typing import Any, Dict, Optional
+from typing import Any, Dict
 
 from pydantic import Field, PrivateAttr
-from rich.tree import Tree
 
 from crewai.task import Task
 from crewai.telemetry.telemetry import Telemetry