Remove now-unused desktop_network_notification needle

Dropped the use of this in the recent notification simplification,
but forgot to remove the needle. Should've run tox...

Signed-off-by: Adam Williamson <awilliam@redhat.com>

needles/kde/desktop_network_notification-kde-20190214.json

@@ -1,16 +0,0 @@
-{
-  "area": [
-    {
-      "type": "match",
-      "xpos": 643,
-      "height": 21,
-      "width": 133,
-      "ypos": 478
-    }
-  ],
-  "properties": [],
-  "tags": [
-    "DESKTOP-kde",
-    "desktop_network_notification"
-  ]
-}