mlxsw: spectrum: Remove unused function declarations

mlxsw: spectrum: Remove unused function declarations

Commit c3d2ed93b14d ("mlxsw: Remove old parsing depth infrastructure")
left behind mlxsw_sp_nve_inc_parsing_depth_get()/mlxsw_sp_nve_inc_parsing_depth_put().
And commit 532b49e41e64 ("mlxsw: spectrum_span: Derive SBIB from maximum port speed & MTU")
remove mlxsw_sp_span_port_mtu_update()/mlxsw_sp_span_speed_update_work() but leave the
declarations.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/20230803142047.42660-1-yuehaibing@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>