mlx4: Remove unused functions

mlx4: Remove unused functions

The last use of mlx4_find_cached_mac() was removed in 2014 by
commit 2f5bb473681b ("mlx4: Add ref counting to port MAC table for RoCE")

mlx4_zone_free_entries() was added in 2014 by
commit 7a89399ffad7 ("net/mlx4: Add mlx4_bitmap zone allocator")
but hasn't been used. (The _unique version is used)

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Link: https://patch.msgid.link/20250203185229.204279-1-linux@treblig.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>