remove datadog_apm role

[joe-lipson]

Tracer download and param injection is now being done in ansible/roles/exec-jar/templates/service.conf which is a better place. Check for apps that are still using the datadog_apm role and see if they are served by using exec-jar. can also remove datadog_apm specific vars in the inventories https://github.com/AtlasOfLivingAustralia/ansible-inventories/blob/master/image-service/image-service-test-cognito.yml#L171-L176