Issue 0011826: Remove ajax_api

ajax_api was used in two places (bug_update_page and tag_update_page)
for the purpose of hiding user selection comboboxes until clicked upon.
This approach relied upon inline JavaScript which is being removed in
1.3.x. It was easier to remove this feature than to reimplement it using
jQuery. It's disputable as to whether anything has been lost (some would
say that the AJAX click-to-edit added more clicks and more delay to
updating forms).