linux: remove linux osi_alloc hash stats

The bucket stat vector is maintained but never read. And it is
occasionally annoying since it can flood messages with
"afs_get_hash_stats: Warning! exceeded max bucket len ..."
Remove it.

Change-Id: Ibc2101c038e40c9ff6ab0401c89fd41af75ed831
Reviewed-on: http://gerrit.openafs.org/9937
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>