As Saurabh says, you can't disable it but you can chose to hide them in your menu. However, that won't hide all of them in Workspace etc...
Most of those send on the image request, you could actually flush them in doPlugins just before the server call are generated. However, you can't flush all and I think it is a little shaky solution...
What are you trying to archive and why don't you want those out of the box variables set?
The best solution would properly be to engage with Engineering Services, who via a VISTA rule may be able to clear most/all of what you want. But again, why would you do so?
/Løjmann