Now that rxe_mcast.c has it's own red-black tree support there is no
longer any requirement for key'ed objects in rxe pools. This patch removes
the key APIs and related code.

Link: https://lore.kernel.org/r/20220208211644.123457-7-rpearsonhpe@gmail.comSigned-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>