Tyap/remove health manager next

This branch removes health_manager_next from cf-release.  

We also noticed the following documentation, which should be updated to no longer mention the old health manager:
https://github.com/cloudfoundry/dea_ng/blob/master/README.md#dea
https://github.com/cloudfoundry/cf-release/blob/master/README.md#cloud-foundry-components-v2
https://github.com/cloudfoundry/cf-release/blob/master/jobs/cloud_controller_ng/spec#L161

We didn't make the doc changes because we felt runtime may want to have a discussion about them first.