nvme-loop: Remove duplicate call to nvme_remove_namespaces

nvme_uninit_ctrl already does that for us. Note that we
reordered nvme_loop_shutdown_ctrl with nvme_uninit_ctrl
but its safe because we want controller uninit to happen
before we shutdown the transport resources.

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