Unable to remove servers from Backup Exec

Double-click on the servers which are no longer required. On the left side, click on each section (Jobs, Job History, Backup Sets). If there is any data available when you click on these sections, right-click and delete them. And then try to remove the server from the backup & restore tab. (Deleting backup sets if present will not allow restores for such servers)
 

Be aware that you cannot delete disk backup sets in BE 2014.  You can only expire them, but it is the same thing.  DLM will purge any expired backup sets from your disk and you would not be able to get them back, so be careful when you expire disk backup sets.

For tape backup sets, you can delete them and they would be removed from the console.  If the tapes are not overwritten, then you can inventory and catalog the tapes to get back the backup sets.