RDMA: Remove 'max_fmr'

Now that FMR support is gone, this attribute can be deleted from all
places.

Link: https://lore.kernel.org/r/12-v3-f58e6669d5d3+2cf-fmr_removal_jgg@mellanox.com


Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Bernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>