RDMA/rxe: Remove unused RXE_MR_TYPE_FMR

This is a left over from the past. It is no longer used.

Link: https://lore.kernel.org/r/20201009165112.271143-1-rpearson@hpe.com


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