IB/qib: remove qib_keys.c

qib_keys.c was left uncompilable in commit 7c2e11fe ("IB/qib: Remove qp and mr functionality from qib")
Since nothing need it, remove it from tree.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>