LU-5727 ldlm: revert the changes for lock canceling policy

LU-5727 ldlm: revert the changes for lock canceling policy

The changes for LRU lock policy was introduced by commit bfae5a4e,
where I was trying to revise the policy to pick locks for canceling.

However, this caused two problems as mentioned in LU-5727. The first
problem is that the lock can only be picked for canceling only if
the number of LRU locks is over preset LRU number AND it's aged; the
second problem is that mdc_cancel_weight() tends to not cancel OPEN
locks, therefore open locks can be kept forever and finally exhausts
memory on the MDT side.

The first problem is fixed by patch e8812867. This patch will revert
the rest of changes related to LRU policy revise.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Ie1dbcd15dc6e739d01ddcae01d7e637688a1d4b2
Reviewed-on: http://review.whamcloud.com/12733
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>