pc: Add a comment explaining why pc_compat_2_4() doesn't exist pc_compat_2_4() doesn't exist, and we shouldn't create one. Add a comment explaining why the function doesn't exist and why pc_compat_*() functions are deprecated. Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>