Remove Google CDN reference for jQuery

http://statichtml.com/2011/google-ajax-libraries-caching.html

According to that, there is a very little benefit to using the
Google CDN to serve jQuery source.  A better option would be to
encourage devs to minify and concatenate all of their script files
into one JS file served with a long-lived cache time.

This was referenced by Alex Sexton (@SlexAxton) in his talk at
jQueryTO March 2nd, 2013.