Don't add-epel on Amazon Linux

The (add-epel :version "5-4") call fails for Amazon Linux. It's a bizarre failure:

    Could not resolve host: download.fedora.redhat.com; Name or service not known

In a shell, on that same Amazon Linux machine:

    $ host download.fedora.redhat.com
    Host download.fedora.redhat.com not found: 3(NXDOMAIN)

Amazon is doing something funky. Anyway, adding EPEL is not needed for `git` (nor a bunch of other things) on Amazon Linux. The standard `yum` sources include many recent packages. `yum install git-core git-email` works just fine.

I don't know the history of Amazon Linux. Maybe there was a time where adding EPEL was the right thing to do? Might someone actually use some older Amazon Linux where that is needed? I don't know how to get answers to these questions.