LU-4416 mem: truncate_pagecache oldsize removed

LU-4416 mem: truncate_pagecache oldsize removed

truncate_pagecache doesn't need oldsize parameter anymore.
In fact, the oldsize useless in all kernel we supported. so
just remove all things relate to it.

Signed-off-by: yang sheng <yang.sheng@intel.com>
Change-Id: Iba9ccebb73e7e8df3179ef1d68507b7403b117a7
Reviewed-on: http://review.whamcloud.com/8800
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>