Bug 661604 - Re-enable this test because it works now. rs=wchen and try

dom/security/test/cors/mochitest.ini

@@ -9,4 +9,3 @@ support-files =
 [test_CrossSiteXHR.html]
 [test_CrossSiteXHR_cache.html]
 [test_CrossSiteXHR_origin.html]
-skip-if = buildapp == 'b2g' || e10s # last test fails to trigger onload on e10s/b2g