[spec] Remove Deployment::Source specs

The R10K::Deployment::Source specs were tagged as :integration because
they would interact with the filesystem and network, and thus were never
run. Since the class being tested has been removed and replaced these
tests are no longer relevant in addition to no longer being run.
Merge pull request #263 from adrienthebo/maint/master/remove-deployment-source-specs

[spec] Remove Deployment::Source specs