nvme-rdma: Remove duplicate call to nvme_remove_namespaces

nvme_uninit_ctrl already does that for us. Note that we reordered
nvme_rdma_shutdown_ctrl and nvme_uninit_ctrl, this is perfectly
fine because we actually want ctrl uninit (aen, scan cancellation
and namespaces removal) to happen before we shutdown the rdma
resources.

Also, centralize the deletion work and the dead controller removal
work code duplication into __nvme_rdma_shutdown_ctrl that accepts
a shutdown boolean.

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