Remove the server outline view delegate

The implementation of the server outline view used to be split between
the view and the window controller. For this we needed an additional
delegate method that returned the contextual menu associated with a
particular row number. We have however concentrated everything to the
view and by doing that removed the need for the additional delegate
method.

Remove the delegate method, and remove the delegate as well since it
lacks methods. We still need to implement the NSOutlineViewDelegate
protocol. Removing our own delegate subclass makes this more clear.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>