Remove old post components code and update tests

[nevyangelova]

Summary

Part of https://mattermost.atlassian.net/browse/MM-43162 is to remove unused old components code, adjust styles, fix unit tests, e2e tests. This PR will handle this

[x] - Removed old post components [x] - Updated unit tests and snapshots [] - Added new unit tests [] - Updated e2e tests

Ticket Link

https://mattermost.atlassian.net/browse/MM-43162

Related Pull Requests

https://github.com/mattermost/mattermost-webapp/pull/11127

Release Note

Removed all post components in favour of a unified approach