Revert of [gn] Switch custom snapsot bot to gn (patchset #2 id:20001 of https://codereview.chromium.org/2113583002/ )

Reason for revert:
Breaks...

Original issue's description:
> [gn] Switch custom snapsot bot to gn
>
> BUG=chromium:474921
> NOTRY=true
>
> Committed: https://crrev.com/52a43518abe9143a14ded92a89bd3384a47e9193
> Cr-Commit-Position: refs/heads/master@{#37431}

TBR=yangguo@chromium.org,vogelheim@chromium.org,jochen@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:474921

Review-Url: https://codereview.chromium.org/2107423003
Cr-Commit-Position: refs/heads/master@{#37434}