Remove the ancient and unsafe FMR method.

Link: https://lore.kernel.org/r/9-v3-f58e6669d5d3+2cf-fmr_removal_jgg@mellanox.comReviewed-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>