io_uring/futex: always remove futex entry for cancel all

We know the request is either being removed, or already in the process of
being removed through task_work, so we can delete it from our futex list
upfront. This is important for remove all conditions, as we otherwise
will find it multiple times and prevent cancelation progress.

Cc: stable@vger.kernel.org
Fixes: 194bb58c ("io_uring: add support for futex wake and wait")
Fixes: 8f350194 ("io_uring: add support for vectored futex waits")
Signed-off-by: Jens Axboe <axboe@kernel.dk>