St: don't attempt to give focus to non reactive actors

Non reactive actors don't expect to be interacted with, and thus
should not get keyboard focus.

https://bugzilla.gnome.org/show_bug.cgi?id=619955

js/ui/networkAgent.js

@@ -165,7 +165,6 @@ const NetworkSecretDialog = new Lang.Class({
         }
 
         this._okButton.button.reactive = valid;
-        this._okButton.button.can_focus = valid;
     },
 
     _onOk: function() {