How to hide Input Format Options and help text under a textarea?
You can use hook_form_alter in a custom module to do this.

For instance, in drupal 7:

// hook_form_alter function
function CUSTOM_MODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
    // We want this on a specific node type
    if ($form_id == 'NODE_TYPE_node_form') {
        $form['#after_build'][] = 'CUSTOM_MODULE_NODE_TYPE_node_form_after_build';
    }
}

// afterbuild function
function CUSTOM_MODULE_NODE_TYPE_node_form_after_build($form) {
    // We want this on a specific field
    $form['YOUR_FIELD']['und']['0']['format']['#access'] = FALSE;
    return $form;
}