remove require_once on api.php

A while back the code got changed so that calling civicrm_initialize() causes api.php to be loaded so the

require_once 'api/api.php';

is redundant.

(the pattern has been copied & pasted enough that it has hung even though it was probably never required in a stable release)

= array()) {
civicrm_initialize();
require_once 'api/api.php';