Revert of Reland changes to v8_snapshot GN build arg. (patchset #2 id:20001 of https://codereview.chromium.org/1979883002/ )

Reason for revert:
Blocks the roll again:
https://codereview.chromium.org/1993163002/

https://build.chromium.org/p/tryserver.chromium.linux/builders/chromeos_amd64-generic_chromium_compile_only_ng/builds/140169

Lets add chromeos_amd64-generic_chromium_compile_only_ng on a reland as well.

Original issue's description:
> Reland changes to v8_snapshot GN build arg.
>
> This patch re-lands #36193 with a couple of minor tweaks
> including updating the BUILD.gn file to use the new
> variable name and incorporating thakis' request to support
> cross-compiling the win snapshot from a mac.
>
> R=thakis@chromium.org, jochen@chromium.org, machenbach@chromium.org
> BUG=608596, 595653
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:chromeos_daisy_chromium_compile_only_ng
>
> Committed: https://crrev.com/b6168e1223d266dba1a357a921bc84ae97a1d803
> Cr-Commit-Position: refs/heads/master@{#36342}

TBR=jochen@chromium.org,thakis@chromium.org,stevenjb@chromium.org,adamk@chromium.org,dpranke@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=608596, 595653

Review-Url: https://codereview.chromium.org/1996533002
Cr-Commit-Position: refs/heads/master@{#36347}