Do not hide visibility checkbox on readonly password

Closes #13165
(grafted from d5e4cb50c2bcfd90ab0e8b09679f5b435bbb681e)

--HG--
branch : 6.0

tryton/tryton/gui/window/view_form/view/form_gtk/char.py

@@ -170,10 +170,5 @@ class Password(Char):
         self.widget.pack_start(
             self.visibility_checkbox, expand=False, fill=True, padding=0)
 
-    def _readonly_set(self, value):
-        super(Char, self)._readonly_set(value)
-        self.entry.set_editable(not value)
-        self.visibility_checkbox.props.visible = not value
-
     def toggle_visibility(self, button):
         self.entry.props.visibility = not self.entry.props.visibility