[FIX] pad: not able to set pad widget

Before this fix, it was possible to set the widget 'pad'
on char fields but it only worked if the current model
inherited from 'pad.common'.
In the other cases, it crashed on closing Studio.

As there is two models only (project.task and
note.note), we decided to remove the possibility to set
this widget in Studio.

opw-745997

addons/pad/static/src/js/pad.js

@@ -13,7 +13,6 @@ var FieldPad = AbstractField.extend({
     events: {
         'click .oe_pad_switch': '_onToggleFullScreen',
     },
-    supportedFieldTypes: ['char'],
 
     /**
      * @override