Deprecate `admit` constraint
Replace with `admit_ips` and `admit_hostnames`
Ref: https://github.com/cfengine/core/commit/8bf5633b868e2e326ae0feb5b15e15ed545bd9f6
Closes: https://cfengine.com/dev/issues/4136
Merge pull request #97 from cfengine/cleanup/4136

Deprecate `admit` constraint