Remove rewrite for iPhone/iPod to /view/iphone

This endpoint doesn't seem to exist, the gist I had copied the nginx
config from must have been out of date. Instead, just serve the
full site, which is now somewhat responsively designed.

Auditors: csilvers

Test Plan:
I updated the config on the jenkins machine and ran "sudo service nginx restart"

Then I set Chrome to emulate the iPhone 5 then visited
jenkins.khanacademy.org and saw that I was served the full page instead
of a 403 error.