fixed linting issues

backend/modules/calendar/api.py

@@ -5,7 +5,6 @@ from datetime import datetime
 from typing import List, Optional
 from modules.auth.dependencies import get_current_user
 from core.database import get_db
-from core.exceptions import not_found_exception
 from modules.auth.models import User
 from modules.calendar.schemas import CalendarEventCreate, CalendarEventUpdate, CalendarEventResponse
 from modules.calendar.service import create_calendar_event, get_calendar_event_by_id, get_calendar_events, update_calendar_event, delete_calendar_event