Consolidate window tracking filters between app monitor and overview.

The windows we considered for both the app monitor and the overview
workspaces were the same, but the code was duplicated once in C, once
in Javascript.

js/ui/workspaces.js

@@ -745,11 +745,8 @@ Workspace.prototype = {
 
     // Tests if @win should be shown in the Overview
     _isOverviewWindow : function (win) {
-        let wintype = win.get_window_type();
-        if (wintype == Meta.WindowType.DESKTOP || 
-            wintype == Meta.WindowType.DOCK)
-            return false;
-        return !win.is_override_redirect();
+        let appMon = Shell.AppMonitor.get_default()
+        return appMon.is_window_usage_tracked(win.get_meta_window());
     },
 
     _createWindowIcon: function(window) {