net/mlx5: Remove unused events callback and logic

The mlx5_interface->event callback is not used by mlx5e/mlx5_ib anymore.

We totally remove the delayed events logic work around, since with
the dynamic notifier registration API it is not needed anymore, mlx5_ib
can register its notifier and start receiving events exactly at the moment
it is ready to handle them.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>