From XenApp 5.0, we could run the chfarm command to remove and add a server to a farm. This command is no longer a valid method from XenApp 6.x.
From Delivery Services Console if we remove the server from the farm, it only removes the server from farm so that it is not visible in the console. However, the server is not completely removed from the data store. So the most effective method of removing a server from a farm is to use the XenApp Server role manager. Select “Leave the current server farm” from the Citrix XenApp Server Configuration window.