Fix: absent state removing whole cron.d file instead of specific job

I've found a critical bug in cron module. If you try to remove some job from cron.d, the ansible will run crontab.remove_job_file() and delete the whole file which contains other jobs. I don't understand what the meaning of this function and commit 8f14ffe5, where this function was appeared, doesn't clarify at all. Furthermore, I think that removing files not a functional that cron module must to do. The file module is exists for this purpose.