Remove references to 'atomic build'

[aweiteka]

We have some examples[1] that specify building an atomic app. I think this is a leftover from a previous behavior.

[1] https://github.com/projectatomic/nulecule/blob/master/examples/guestbook-go/README.md https://github.com/projectatomic/nulecule/blob/master/examples/redis-centos7-atomicapp/README.md