RDMA/uverbs: Cleanup wq/srq context usage from uverbs layer

Both wq_context and srq_context are some leftover from the past in uverbs
layer, they are not really in use, drop them.

Link: https://lore.kernel.org/r/20200506082444.14502-5-leon@kernel.org


Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>