Fix dialog hiding on row-activate signal in WinForm

The fixed issue appeared only on screens using WinForm, like the attachment list
opened from the toolbar. Screens used on a tab are not affected.

issue2266
review201002
(transplanted from e19c447ee16c52f540da1d77e5dd1630e94eef48)

tryton/gui/window/view_form/screen/screen.py

@@ -288,12 +288,6 @@ class Screen(SignalEvent):
 
     def default_row_activate(self):
         from tryton.action import Action
-        from tryton.gui.main import Main
-        main = Main.get_main()
-        current_form = main.get_page()
-        if current_form:
-            for dialog in current_form.dialogs:
-                dialog.hide()
 
         if (self.current_view.view_type == 'tree' and
                 self.current_view.widget_tree.keyword_open):