Remove cronjobs file

This is now being handled by pp-deployment as this is configuration
specific to our deployment rather than intrinsic to the application.
Now in:
pp-deployment/environments/common/app_config/backdrop-ga-realtime-collector/cronjobs
Merge pull request #19 from alphagov/remove-cronjobs-file

Remove cronjobs file - now being handled here pp-deployment/environments/common/app_config/backdrop-ga-realtime-collector/cronjobs