fix: Refactor chat_service.py and remove unused code (#2530)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

backend/modules/chat/service/chat_service.py

@@ -123,7 +123,7 @@ class ChatService:
         chat_id: UUID,
     ) -> List[ChatItem]:
         chat_history = self.get_chat_history(str(chat_id))
-        chat_notifications = notification_service.get_chat_notifications(chat_id)
+        chat_notifications = []
         return merge_chat_history_and_notifications(chat_history, chat_notifications)
 
     def get_user_chats(self, user_id: str) -> List[Chat]:

backend/modules/notification/service/notification_service.py

@@ -1,6 +1,3 @@
-from typing import List
-from uuid import UUID
-
 from models.settings import get_supabase_client
 from modules.notification.dto.inputs import NotificationUpdatableProperties
 from modules.notification.entity.notification import Notification
@@ -23,12 +20,6 @@ class NotificationService:
         """
         return self.repository.add_notification(notification)
 
-    def get_chat_notifications(self, chat_id: UUID) -> List[Notification]:
-        """
-        Get notifications by chat_id
-        """
-        return self.repository.get_notifications_by_chat_id(chat_id)
-
     def update_notification_by_id(
         self, notification_id, notification: NotificationUpdatableProperties
     ):