gistfile1.txt

<?php

foreach ($form->getFieldsets() as $group => $fieldset) {
    foreach ($form->getFieldset($group) as $field) {
        $form->removeField($field->fieldname); // This will remove only the fields outside <fields> elements
        // $form->removeField($field->fieldname, $group); // This will remove only the fields inside the <fields> element
    }
}

?>


<form>

    <fieldset name="testa">
        <field..../>
        <field..../>
        <field..../>
    </fieldset>

    <fieldset name="testb">
        <field..../>
        <field..../>
        <field..../>
    </fieldset>

    <fields name="testc">
        <fieldset label="testc">
            <field..../>
        </fieldset>
    <fields>

</form>