Support sync loading of binary files via enyo.Ajax

If you attempted to load binary files with enyo.Ajax synchronously,
the code kept trying to access xhr.responseText which is not a valid
thing to do because the response comes in xhr.response instead. This
would throw an error and make it impossible to load any binary file
synchronously.
Took out the check for binary sync requests

Took out the check for whether or not the request is synchronous when
figuring out what the return property is for loading binary files. The
binary file return property is the same for both sync and async
requests anyways.
this is actually the correct way to handle this synchronous request as the onreadystatechange is an overloaded method

Enyo-DCO-1.1-Signed-Off-By: Cole Davis (cole.davis@lge.com)
Merge pull request #728 from enyojs/BHV-8308-coledavis

Fix for: BHV-8308

Reviewed-by: Aaron Tam (aaron.tam@lge.com)