nvme-rdma: remove nvme_rdma_remove_ctrl

It is only used in two places, and some of the work done by it will
be taken into common code soon.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>