MAINTAINERS: Drop stale F: from "Linux io_uring"

We neglected to update MAINTAINERS when we dropped stubs/io_uring.c. Update it now. Fixes: 047dabef97 (block/io_uring: use aio_add_sqe(), 2025-11-03) Cc: Julia Suvorova <jusual@redhat.com> Cc: Stefan Hajnoczi <stefanha@redhat.com> Cc: Stefano Garzarella <sgarzare@redhat.com> Cc: qemu-block@nongnu.org Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Message-ID: <20260603064032.3733394-35-armbru@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>