p9auth: remove this test

p9auth module was just included in staging for a while.
It had been removed from kernel due to lack of interest
(commit 2d629030ca649bd4a7356befedbe7bbefa840b21)
Remove it from LTP.

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
Acked-by: Jan Stancek <jstancek@redhat.com>