chore: Remove logging that contains full event data from DatabaseSessionService

Resolves #2153

PiperOrigin-RevId: 794288546

Author: DeanChensj

src/google/adk/sessions/database_session_service.py

@@ -548,8 +548,6 @@ async def delete_session(
 
   @override
   async def append_event(self, session: Session, event: Event) -> Event:
-    logger.info(f"Append event: {event} to session {session.id}")
-
     if event.partial:
       return event