mlxsw: spectrum: Drop unused functions mlxsw_sp_port_lower_dev_hold/_put()

As of commit 151b89f6 ("mlxsw: spectrum_router: Reuse work neighbor
initialization in work scheduler"), the functions
mlxsw_sp_port_lower_dev_hold() and mlxsw_sp_port_dev_put() have no users.
Drop them.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/d0adcd7cb4ea19416294a0f861100edba84c9f36.1690471774.git.petrm@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>