vCenter Object List & extensionList with NetBackup

We have an issue with our vCenter and the number of objects it's having to manage. VMWare are thumbing several NetBackup extensions registered on the vCenter.

Has anyone ever come accross: extensionList["com.vmware.netbackup.NetBackup_x.x"]

We have several of these entries related to all the levels of Netbackup we've ever had installed in the environment however all our master and media servers are at 8.0.

We want to unregister as many as we can but there doesn't seem to be any documentation regarding what these extensions are or how they operate. Any previous insight would be very appreciated.