dma-buf/fence: kerneldoc: remove unused struct members

Commit 0431b906 ("staging/android: bring
struct sync_pt back") removed child_list and active_list from struct fence,
but left it in kernel doc. Delete them.

Fixes: 0431b906

 ("staging/android: bring struct sync_pt back")

Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1470912480-32304-2-git-send-email-sumit.semwal@linaro.org