common/populate: remove unnecessary devices directory creation

_scratch_ext4_populate and _scratch_xfs_populate try to create
devices directory in xfstests/, so if we run xfs/083 or ext4/006
twice, it'll fail, fix this issue.

Signed-off-by: Xiaoguang Wang <wangxg.fnst@cn.fujitsu.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

common/populate

@@ -141,7 +141,6 @@ _scratch_xfs_populate() {
 
 	# Char & block
 	echo "+ special"
-	mkdir devices
 	mknod "${SCRATCH_MNT}/S_IFCHR" c 1 1
 	mknod "${SCRATCH_MNT}/S_IFBLK" c 1 1
 
@@ -241,7 +240,6 @@ _scratch_ext4_populate() {
 
 	# Char & block
 	echo "+ special"
-	mkdir devices
 	mknod "${SCRATCH_MNT}/S_IFCHR" c 1 1
 	mknod "${SCRATCH_MNT}/S_IFBLK" c 1 1