IB/mlx5: Remove old FRWR API support

No ULP uses it anymore, go ahead and remove it.
Keep only the local invalidate part of the handlers.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Doug Ledford <dledford@redhat.com>