RDMA/rxe: Remove unneeded RXE_POOL_ATOMIC flag

Remove RXE_POOL_ATOMIC flag from rxe_type_info for AH objects.  These
objects are now allocated by rdma/core so there is no further reason for
this flag.

Link: https://lore.kernel.org/r/20201216231550.27224-2-rpearson@hpe.com


Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>