net/mlx5e: Remove unused function mlx5e_sq_xmit_simple

The last usage was removed as part of
commit 40379a00 ("net/mlx5_fpga: Drop INNOVA TLS support").

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>