[SCSI] libsas: Remove SAS_TASK_INITIATOR_ABORTED flag

This flag is no longer necessary because we push tasks to be aborted into
the EH as soon as we possibly can, and let the SCSI EH code take care of
the coordination for which this flag was used.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>