Revert "LU-5275 lprocfs: remove last of non seq data structs and functions."

This reverts commit 0ad4f8a4227ed7dd93fec99d33c6bb25056473fc.
This patch has broken the el6.6 build:
include/linux/proc_fs.h:120: note: previous declaration of 'remove_proc_subtree' was here

Change-Id: I62d9b032448d9eea5d089b69382c2ff5064c5d3d
Reviewed-on: http://review.whamcloud.com/12953
Tested-by: Jenkins
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>