Remove controls implemented natively from "non-native" list

Both GtkSearchEntry and GtkCalendar are used in wxGTK whenever possible.

docs/gtk/nonnative.txt

@@ -1,14 +1,8 @@
 List of classes which should use their native GTK+ equivalents but don't:
 
-- wxSearchCtrl
-    Should use GtkSearchEntry (GTK+ 3.6+)
-
 - wxStatusBar:
     Problem with multiple fields, GtkStatusbar only seems to support one pane
 
-- wxTreeCtrl
-    Ryan Norton has implemented this
-
 - wxListCtrl
     Could be reimplemeted in terms of wxDataViewCtrl?
 
@@ -19,9 +13,5 @@ List of classes which should use their native GTK+ equivalents but don't:
     supports both and can even change orientation at
     runtime.
 
-- wxDatePickerCtrl
-- wxCalendarCtrl
-    Use GtkCalendar
-
 - wxWizard
     Can GtkAssistant be used?