RDMA/iw_cxgb3: Remove the iw_cxgb3 module from kernel

Remove iw_cxgb3 module from kernel as the corresponding HW Chelsio T3 has
reached EOL.

Link: https://lore.kernel.org/r/20190930074252.20133-1-bharat@chelsio.com


Signed-off-by: Potnuri Bharat Teja <bharat@chelsio.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>