gui: Dont catch SIGWINCH.

gui: Dont catch SIGWINCH.

This is unnecessary since the curses library generates a KEY_RESIZE
event on SIGWINCH anyway. Hence window change events can be handled
as well in the normal input processing function. This allows to remove
the SIGWINCH part of the signal handling code.

Another advantage of handling SIGWINCH in the same way as normal
input events is that it is easier to propagate the event. This will
turn out to be useful for the upcoming gui menu changes.