E.g. KVM_{CREATE,GET,SET}_PIT are good examples of obsolete ioctls; they've been
supplanted by newer variants, but KVM still supports the old ones too.
Alternatively (to marking them deprecated), can we completely remove all references
to VM_SET_MEMORY_REGION and KVM_SET_MEMORY_ALIAS? The cascading updates in api.rst
will be painful, but it's one-time pain.