Revert "assistant: update watch list to new list"

This reverts commit 3ae69fd.

Reason for revert: seem gerrit does not deliver email to @google.com
group, at least this one, for some reason.

Original change's description:
> assistant: update watch list to new list
> 
> Bug: None
> Change-Id: I96830b2da441d7c0d1750c62a5653d266b7fc18e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2048539
> Reviewed-by: Tao Wu <wutao@chromium.org>
> Commit-Queue: Xiaohui Chen <xiaohuic@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#740101}

TBR=xiaohuic@chromium.org,wutao@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: None
Change-Id: Ia84049cfe239c1af3f33ab7fbd5b679e4d2e27c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2068866
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Commit-Queue: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743725}

WATCHLISTS

@@ -2081,7 +2081,7 @@
     'arc_video_accelerator': ['hiroh+watch@chromium.org'],
     'ash': ['kalyan.kondapally@intel.com',
             'sadrul@chromium.org'],
-    'assistant': ['croissant-eng+reviews@google.com'],
+    'assistant': ['croissant-eng+reviews@chromium.org'],
     'audio_service': ['marinaciocea+watch@chromium.org',
                       'olka+watch@chromium.org'],
     'aura': ['kalyan.kondapally@intel.com',