selftests: mlxsw: sharedbuffer: Remove duplicate test cases

selftests: mlxsw: sharedbuffer: Remove duplicate test cases

On both port_tc_ip_test() and port_tc_arp_test(), the max occupancy is
checked on $h2 twice, when only the error message is different and does not
match the check itself.

Remove the two duplicated test cases from the test.

Fixes: a865ad999603 ("selftests: mlxsw: Add shared buffer traffic test")
Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Link: https://patch.msgid.link/d9eb26f6fc16a06a30b5c2c16ad80caf502bc561.1733414773.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>