Kill off dummy kbd drivers

As far as I can tell, these are an artifact of times when linker sets
couldn't be empty, otherwise the kernel build would fail due to unresolved
symbols. hselasky fixed this in r268138, and I've audited the kbd portions
to make sure nothing would blow up due to the empty linker set and
successfully compiled+ran a kernel with no keyboard support at all.

Kill them off now since they're no longer required.

MFC after: 1 week