net/mlx5: Remove unused mlx5_core_health member recover_work

The code related to health->recover_work was removed in
commit 63cbc552 ("net/mlx5: Handle SW reset of FW in error flow")

Fix struct mlx5_core_health accordingly.

Signed-off-by: Mikhael Goikhman <migo@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>