LU-6426 lustre: remove EIOCBRETRY handling

LU-6426 lustre: remove EIOCBRETRY handling

With linux commit 41003a7bcfed1255032e1e7c7b487e505b22e298
AIO retry handling was removed due to it being buggy and no
one using it, including lustre. Since this is the case
remove EIOCBRETRY since it no longer in the kernel starting
with version 3.18.

Change-Id: Icdc2de3fe252a6315914b906ef29c80343aa93e8
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: http://review.whamcloud.com/14507
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Blake Caldwell <blakec@ornl.gov>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Thomas Stibor <thomas@stibor.net>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>