Revert "xen/privcmd: create address space to allow writable mmaps"

This reverts commit 24a89b5b.

We should no longer need an address space now that we're correctly
setting VM_PFNMAP on our vmas.

Conflicts:

	drivers/xen/xenfs/super.c

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>