RDMA/irdma: Delete unused struct irdma_bth

The struct irdma_bth is not used, so remove it.

Link: https://lore.kernel.org/r/20211006201531.469650-1-yanjun.zhu@linux.dev


Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Acked-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>