remove the define.amd.jQuery check

For 2.0 consideration:

Removes the `define.amd.jQuery` check in the AMD registration. In practice, AMD loaders just set this anyway as they wanted to load jQuery, and any error as a result of the loader not properly accounting for multiple jQuerys in the page would show up as loader errors. 

The loader gets blamed for the error, as it should, and jQuery does not. So removing it as it has become superfluous, and was probably an overly cautious measure.