[BUG] Persistent note is not removed from database using `?delete <message_id>` command.

[Jerrie-Aries]

Describe the bug
Persistent note is not removed from DB using?delete <message_id> command.

Bot Info
Bot version (check with @modmail about): 3.9.4
Host method (Heroku, self-host, etc): Heroku, Self Host

To Reproduce
Steps to reproduce the behavior:

1. Who can reproduce (ex. anyone, owners)?
   Supporter
2. Where can it be reproduced (ex. in thread channels, recipient DM's)?
   Thread channel
3. Done what to cause the error?
   Delete the persistent note from thread channel using ?delete <message_id> command. The note message got deleted, however it was not removed from the database. So every times the recipient opens a new thread, the persistent note will be sent in thread channel.
4. Any recently made changes to your bot?
   None.
5. Errored
   No error, the bot just returned silently after removing the note from thread channel.

Additional context
According to this in thread.py:
https://github.com/kyb3r/modmail/blob/3717df646644159c5a0e713aa83bfcdbf768dcdb/core/thread.py#L668-L669
the bot should remove the note from the database.