Revert of [gn] Switch linux64 debug and internal snapshot to gn (patchset #1 id:1 of https://codereview.chromium.org/2105353002/ )

Reason for revert:
Breaks...

Original issue's description:
> [gn] Switch linux64 debug and internal snapshot to gn
>
> BUG=chromium:474921
>
> Committed: https://crrev.com/3cfc9f209ed0c173319659114859b7e848812fd7
> Cr-Commit-Position: refs/heads/master@{#37414}

TBR=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/2109503007
Cr-Commit-Position: refs/heads/master@{#37420}