Downloaded Ruby binary isn't cleared after installing

In my opinion it is best to clear out the downloaded `ruby-x.x.x.tar.bz2` binary file after we extracted it into the `rbenv/versions` directory. This will clean up the `versions` directory and it will allow easy re-installing of binaries by just removing the `versions/x.x.x` directory. After that our Chef cookbooks will re-download a new `.tar.bz2` and extract it in the new location.
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