asyncTest() is deprecated

[notmessenger]

http://api.qunitjs.com/QUnit.asyncTest/

There are several uses of it throughout the codebase. One such example is:

sl-ember-store/tests/unit/adapters/ajax-test.js

Line 90 in a27ccdb

asyncTest( '__find single model with id', function(){

[notmessenger]

Relates to #114