nvme-pci: remove the inline scatterlist optimization

We'll have a better way to optimize for small I/O that doesn't
require it soon, so remove the existing inline_sg case to make that
optimization easier to implement.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>