RDMA/core: Remove ib_find_cached_gid() and ib_find_cached_gid_by_port()

Remove these two functions since all their callers have been removed.
See also commit ea8c2d8f ("RDMA/core: Remove unused ib cache
functions").

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>