Jitsi and 1:1 button clashes in nav bar

[gaelledel]

In 1:1 calls when users add the Jitsi integration, it automatically adds a "join" button in the nav.
This join button is interfering with the other call controls in DM rooms and should therefore be removed.
Let's also remove the "slide to End call". If users want to remove the jitsi widget in 1:1 calls, they can do so via the integration menu.
We can however preserve the call tile in the timeline to allow users to use Jitsi.