Revert "nvk: Advertise KHR_device_group"
This reverts commit cc89262a.
Consider this a bit of a placeholder. This commit causes PBDMA errors for me on Turing TU104 when I run vulkaninfo. When I've got GSP loaded the channel dies and vulkaninfo terminates.
I'm not sure what causes the problem here, but creating the 3rd context seems to be about when things explode. Pre-GSP you should see fails in the dmesg.