Fixes #37: yumrepo::epel doesn't exist anymore.

* Removed inlude_recipe for yumrepo:epel from default recipe.
  - yumrepo v2.0.0 doesn't use it anymore, since it is now in yum
    cookbook (commit 08024f5c665103566cfae6d016a1079c77c0a820 of
    yumrepo).