LU-9114 ldlm: don't compute sumsq for pool stats

LU-9114 ldlm: don't compute sumsq for pool stats

Remove the calculation of sumsq from the LDLM pool stats, since
these stats are almost never used, while conversely the pools
are updated frequently.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I90612b613fb76f4500ca6cd5613f5c121b3ebbe5
Reviewed-on: https://review.whamcloud.com/39435
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>