Remove asset-master cron job already marked as absent
Remove asset-master cron job already marked as absent

These cron job definitions were marked as `ensure => absent` 8 months
ago in this commit [1].  I think it's safe to assume we can remove them
now.

[1]: 8007697ed3ca2b20594b1809073b79950e29d732

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet