assistant: remove a TODO that's done

TBR=xiaohuic@chromium.org

Change-Id: I61ca7fc31d82645e0b49d0083438a6a53531ed39
Reviewed-on: https://chromium-review.googlesource.com/1145731
Reviewed-by: Muyuan Li <muyuanli@chromium.org>
Commit-Queue: Muyuan Li <muyuanli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576988}
1 file changed