[gtk/wip/baedert/for-master: 83/146] docs: Remove widget_system.txt

[Timm Bäder <baedert src gnome org>]

commit 67892289f1885f1b8e41f2776e96011aae4776df
Author: Timm Bäder <mail baedert org>
Date:   Sun Aug 25 08:28:06 2019 +0200

    docs: Remove widget_system.txt
    
    Almost all information in here is incorrect or outdated, most of it is
    still from gtk2 and GtkObject days.

 docs/widget_system.txt | 500 -------------------------------------------------
 1 file changed, 500 deletions(-)