rtsp-client: Don't ever close the client connection directly when a session is torn down

commit 0239b830a182036fa6446b5a7930b872d6423407 (HEAD -> sync-close-client-fixup)
Author: Sebastian Dröge <sebastian@centricular.com>
Date:   Mon Apr 27 23:25:22 2020 +0300

    rtsp-client: Combine the pre-session and post-session timeout
    
    They previously used the same state but different mechanisms and
    functions, which was difficult to follow, error prone and simply
    confusing.
    
    Also adjust the test for the post-session timeout a bit to be less racy
    now that the timing has slightly changed.

commit e1629bab20f6dcf51f37a9641bddccaad9da740d
Author: Sebastian Dröge <sebastian@centricular.com>
Date:   Mon Apr 27 19:47:15 2020 +0300

    rtsp-client: Don't ever close the client connection directly when a session is torn down
    
    There might be other sessions that are running over the same RTSP
    connection and we should not simply close the client directly if one of
    them is torn down.
    
    By default the connection will be closed once the client closes it or
    the OS does. This behaviour can be adjusted with the
    post-session-timeout property, which allows to close it automatically
    from the server side after all sessions are gone and the given timeout
    is reached.
    
    This reverts the previous commit.