Discussions stay forever in the side tab-panel after removing, if you pin their start notification.

Description:

Pinned notifications about a started discussion make this discussion stay forever in the side "Discussions" tab and duplicate itself there.

Steps to reproduce:

1. Start a private channel (group).
2. Send a new message to that channel.
3. Begin a discussion about this message.
4. Pin the notification about started discussion in the main channel.
5. Delete the started discussion.
6. Unpin the notification about started discussion.
7. Open side "Discussions" tab.

Expected behavior:

After I delete the discussion, it should disappear from the "Discussions" side tab.

Actual behavior:

After I deleted the discussion and opened the "Discussions" side tab, I saw two live messages for the deleted discussion. And I cannot even remove these messages from there.

Server Setup Information:

• Version of Rocket.Chat Server: It is open.rocket.chat public server.
• Operating System:
• Deployment Method:
• Number of Running Instances:
• DB Replicaset Oplog:
• NodeJS Version:
• MongoDB Version:

Client Setup Information

• Desktop App or Browser Version: 2.17.11 Windows client and Browser client version (Chrome 85.0.4183.83 x64).
• Operating System: Windows 7 x64 and Windows 10 x64.

Additional context

Relevant logs:

Start by reproducing the seven steps in the Discussions side tab, using the pinned discussion notification as the trigger. Trace how deleting the discussion and unpinning its notification update that tab. Done means the deleted discussion is absent and no duplicate live messages remain.