delete dsh group "broken_appservers"

want to reduce number of useless groups that are edited each time a server is
taken down or added back.

stop me if you think there is a real use for this specific group.

seems to me just removing/readding into mediawiki-installation and apaches
are the ones that matter.

if you think it should actually be used, please add here why:

https://wikitech.wikimedia.org/w/index.php?title=Server_Lifecycle&diff=85189&oldid=83670

Change-Id: Icf6051313a964757083d7dbf93dd910bc3f77bcf
Merge "delete dsh group "broken_appservers"" into production