selftests: mlxsw: Remove qos_burst test

The previous patch added a test which can be used instead of qos_burst.sh.
Remove this test.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>