RDMA/efa: Remove unneeded admin commands abort flow

The admin commands abort flow is buggy (use-after-free) and not really
necessary as it is guaranteed that after ib_unregister_device() is called
there are no user verbs threads running in parallel, delete it.

Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
Reviewed-by: Firas JahJah <firasj@amazon.com>
Reviewed-by: Yossi Leybovich <sleybo@amazon.com>
Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>