LU-4590 ptlrpc: Remove log message about export timer update

LU-4590 ptlrpc: Remove log message about export timer update

Function ptlrpc_update_export_timer generates lots of D_HA level log
messages whenever the export timer gets updated. Those log messages
are found little use for issue investigations, and it will take space
in the Lustre log buffer. We are removing it now.

Xyratex-bug-id: MRP-733
Signed-off-by: Cheng Shao <cheng_shao@xyratex.com>
Change-Id: I3699e81fd4bf0b8677c1fbd09ced5d81ffba3f81
Reviewed-on: http://review.whamcloud.com/9147
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>