remove unnecessary DELETE action for 'set_certified'

[romanblanco]

Fixes: https://pulp.plan.io/issues/5711

[bmbouter]

@romanblanco Thanks for this! I apologize our contributing docs are not fully up to date. To accept this can you do a few small things?

1. Can you file a short issue here with the description: https://pulp.plan.io/projects/ansible_plugin/issues/new
2. Can you include an entry in the CHANGES folder that refers to ^ issue number. See docs here
3. Can you associate your commit with that issue using this syntax in your commit message.

Thanks again, and I'll try to fix these contributing docs for the future.

[bmbouter]

^ should get the CI passing for you

[romanblanco]

@bmbouter please, restart Travis.

[bmbouter]

@romanblanco every time you force push Travis will run. Look at the errors in the job, it's complaining due to black formatting. https://travis-ci.org/pulp/pulp_ansible/jobs/611859747#L440

[bmbouter]

Currently CI is failing on 'master' so even if this PR is perfect it will still fail. So this work is effectively blocked. :( We're going to fix that other problem, and then post back here when this is unblocked.

[daviddavis]

Thank you @romanblanco!