MDL-50937 tag: Stop using deprecated context

$.context has been deprecated for a long time - since before this code was
written. Unfortunately jQuery does not emit anything for deprecated code so
this was not picked up sooner.

lib/amd/src/tag.js

@@ -36,7 +36,7 @@ define(['jquery', 'core/ajax', 'core/templates', 'core/notification', 'core/str'
             $('body').delegate('.tagarea[data-ta] a[data-quickload=1]', 'click', function(e) {
                 e.preventDefault();
                 var target = $(this),
-                    query = target.context.search.replace(/^\?/, ''),
+                    query = target[0].search.replace(/^\?/, ''),
                     tagarea = target.closest('.tagarea[data-ta]'),
                     args = query.split('&').reduce(function(s, c) {
                       var t = c.split('=');