Remove name-spaces from koans on slurp.

There are a couple of proposals (functional-koans/clojure-koans#69, 
functional-koans/clojure-koans#71) that will add a name-space to the koans 
files in order to fix an issue related to the REPL.

If one of these pull request is merged in, then a change like this one
will be needed in order to maintain a pass on `lein koan test`.