[web/test] stop calling loadxhtml with a form.callback
It was deprecated in 3.9 (changeset 7b9553a9db65) and removed in 3.18.
Related to #5533303.
Latest changes
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* table of `all latest changes`_
Links below is providing useful RQL query example.
.. _all latest changes: ../view?rql=Any+M%2CX+WHERE+X+modification_date+M+ORDERBY+M+DESC+LIMIT+30