IB/ocrdma: Removed GID add/del null routines

add_gid() and del_gid() are optional callback routines.
ib_core ignores invoking them while updating GID table entries if
they are not implemented by provider drivers. Therefore remove them.

Reviewed-by: Daniel Jurgens <danielj@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>