securityfs: don't pin dentries twice, once is enough...

[ Upstream commit 27cd1bf1240d482e4f02ca4f9812e748f3106e4f ]

incidentally, securityfs_recursive_remove() is broken without that -
it leaks dentries, since simple_recursive_removal() does not expect
anything of that sort.  It could be worked around by dput() in
remove_one() callback, but it's easier to just drop that double-get
stuff.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>