[REF] web: remove useless code

The utility function xml_to_json, which is mainly used by the views to
parse their arch (from string to xml tree) had a peculiar behaviour: it
tried to process some attributes as json.  If by chance, these
attributes are valid json, then they are replaced by their parsed value.

It is difficult to say why it could be useful.  Maybe this was done to
prevent using pyeval many times later on.  But if that is the case, it
should be done by the view code and not the utility function (the view
can precompute all attributes once).

Also, this behaviour is annoying for code later in the chain, which
needs to check if what it gets is an object or a string.  With this
change, attributes are always returned as string (at this point).

closes odoo/odoo#28133

addons/web/static/src/js/core/utils.js

@@ -427,13 +427,6 @@ var utils = {
                 return (strip_whitespace && node.data.trim() === '') ? undefined : node.data;
             case 1:
                 var attrs = $(node).getAttributes();
-                _.each(['domain', 'filter_domain', 'context', 'default_get'], function (key) {
-                    if (attrs[key]) {
-                        try {
-                            attrs[key] = JSON.parse(attrs[key]);
-                        } catch(e) { }
-                    }
-                });
                 return {
                     tag: node.tagName.toLowerCase(),
                     attrs: attrs,