audit: Remove leftover reference to the audit_tasklet

This was replaced with a kauditd_wait kthread long ago,
back in:

     b7d11258

 (AUDIT: Send netlink messages from a separate kernel thread)

Update the stale comment.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul Moore <paul@paul-moore.com>