net/mlx5: HWS, Cleanup after pool refactoring

Remove members which are now no longer used. In fact, many of the
`struct mlx5hws_pool_chunk` were not even written to beyond being
initialized, but they were used in various internals.

Also cleanup some local variables which made more sense when the API was
thicker.

Signed-off-by: Vlad Dogaru <vdogaru@nvidia.com>
Reviewed-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Link: https://patch.msgid.link/1744312662-356571-6-git-send-email-tariqt@nvidia.com


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