kernfs: remove duplicate dir.c at the top dir

a8fa94e0 ("Merge branch 'master' into
driver-core-next-test-merge-rc2") mistakenly introduced a duplicate
dir.c at the top directory.  Remove it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>