Remove skipper prometheus job
Remove skipper prometheus job

The job skipper_serve_host_duration_2xx was not collecting any data
since #4243, once the requested metric does not have the dimension
required.

This commit is a cleanup removing the job completely. The job is no
longer used in our monitoring systems.

zalando-incubator/kubernetes-on-aws,zalando-incubator/kubernetes-on-aws,zalando-incubator/kubernetes-on-aws