[QA] Incorrect notification functionality upon rejoining a channel

[kwspgoliasz]

Description:
Rejoining a previously left channel during the same session, results in the notifications for messages sent during user's absence getting displayed in the notification box.

Steps to reproduce:

1. Load into Decentraland with two avatars via wallets.
2. Have both avatars join the same channel (ex. help).
3. Write a message on the channel.
4. Leave the channel with one avatar.
5. Write a message on the channel with the second avatar.
6. Rejoin the channel with the first avatar.
7. Observe the issue.

Reproduction rate:
5/5

Results:
Rejoining the channel initiates notifications for messages sent while the user was absent from it.

Expected results:
Lack of notifications for messages sent during user's absence.

Notes:

• The issue can be reproduced only on the wallet account.

• The issue can be reproduced on both the production and development branches.

• Please see the attached video for reference: https://images.zenhubusercontent.com/337227404/2b376305-d0ae-439f-b978-d7b25f65b58a/_3713.mp4.

• Platforms: Web client, Windows client.