delete dsh group 'nagios'

this was once created most likely by me when using upgrade-helper script
to create dsh groups from parsing nagios config as the reliable source.
but it doesn't make sense to keep an outdated version in git.

Change-Id: I83bbc69c6de11e9166c91b0db624e531b31f2570
Merge "delete dsh group 'nagios'" into production