Fix: level strip width is wrong when you start open toonz (#334) (#357)
    
    On the creation the docking panel of the level strip was assigned a minimum

    width. This has no effect, but making the docking panel too big, because the

    size of the underlying controls hasn't been calculated at this point.

    Removing the line fixes the issue with the level strip size, without affecting

    the docking window otherwise.