net/mlx5: Remove unused functions

Remove functions which are no longer used in the driver:
  mlx5e_ipsec_is_tx_flow
  mlx5_health_flush
  get_cqe_enhanced_num_mini_cqes
  get_cqe_l3_hdr_type
  mlx5_health_flush
  mlx5_fs_is_ipsec_flow
  _mlx5_fs_is_outer_ipproto_flow
  mlx5_fs_is_outer_tcp_flow
  mlx5_fs_is_outer_udp_flow
  mlx5_fs_is_vxlan_flow
  mlx5_fs_is_outer_ipsec_flow

Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>