Change contextual filter to a Select list on Pane

file.php

/**
 * Implements hook_form_FORMID_alter().
 */
function ccm_publications_form_views_content_views_panes_content_type_edit_form_alter(&$form, &$form_state) {
  // Change this out to be a select list.
  if (isset($form['arguments']['field_ccm_publication_type_tid'])) {
    $v = taxonomy_vocabulary_machine_name_load('ccm_publication_type');
    $terms = taxonomy_get_tree($v->vid);
    foreach ($terms as $term) {
      $vocab[$term->tid] = $term->name;
    }

    $form['arguments']['field_ccm_publication_type_tid']['#type'] = 'select';
    $form['arguments']['field_ccm_publication_type_tid']['#options'] = $vocab;
  }
}