[web/data] fix treeview regression (closes #3526466) Changeset 68cde7431c2c "[js] remove 3.9 bw compat (where apparently unused)" removed the use of form.callback from loadxhtml, which treeview relied on. Update to add a callback on the loadxhtml return value instead.

drop_relation_definition('CWSourceSchemaConfig', 'cw_schema', 'CWAttribute')
sync_schema_props_perms('cw_schema')