convert securityfs

convert securityfs

securityfs uses simple_recursive_removal(), but does not bother to mark
dentries persistent.  This is the only place where it still happens; get
rid of that irregularity.

* use simple_{start,done}_creating() and d_make_persitent(); kill_litter_super()
use was already gone, since we empty the filesystem instance before it gets
shut down.

Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>