LU-11999 dne: performance improvement for file creation

LU-11999 dne: performance improvement for file creation

This is to remove an obsoleted code where it causes drastic
performance degradation. This code is written before PERM lock
is introduced, and it requests UPDATE lock at path walk for
remote directory, which will be cancelled at later file creation.

Tests result before and after this patch is applied:

Test case:
rm -rf /mnt/lustre_purple/testdir
lfs mkdir -i 0 /mnt/lustre_purple/testdir
lfs mkdir -i 2 /mnt/lustre_purple/testdir/dir2
./lustre-release/lustre/tests/createmany -o \
	/mnt/lustre_purple/testdir/dir2/f 10000

Before the patch is applied:
total: 10000 open/close in 12.82 seconds: 780.22 ops/second

After the patch is applied:
total: 10000 open/close in 4.89 seconds: 2044.75 ops/second

Signed-off-by: Jinshan Xiong <jinshan.xiong@gmail.com>
Change-Id: Ib474dc28d6edc7d15801b6821edc0e1d108bb4b6
Reviewed-on: https://review.whamcloud.com/34291
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Andrew Perepechko <c17827@cray.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>