irdma(4): remove artificial completion generator

Removing artificial completion generator as there had been no indication
of the code being required for E810 cards. Further more it was found
that the code may have unpleasant side effects on user experience when
using ucmatose tool.

Signed-off-by: Bartosz Sobczak <bartosz.sobczak@intel.com>
Signed-off-by: Eric Joyner <erj@FreeBSD.org>

Reviewed by: erj@
Approved by: re (cperciva)
Sponsored by: Intel Corporation
Differential Revision: https://reviews.freebsd.org/D41593

(cherry picked from commit ffafa6a4d157e49e6b12567958c4ab0c9151c080)
(cherry picked from commit 4e80493a33feeabd358ffc233463934a85649c45)