net/mlx4_core: Remove unused *_str functions from the resource tracker

Removed unsued *_str helper functions from resource_tracker.c

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>