Revert of Blink-compatible serialization of arrays, both dense and sparse. (patchset #6 id:100001 of https://codereview.chromium.org/2259633002/ )

Reason for revert:
Broke MIPS compile due to an uninitialization warning:

https://build.chromium.org/p/client.v8.ports/builders/V8%20Mips%20-%20builder/builds/3110/steps/compile/logs/stdio

Original issue's description:
> Blink-compatible serialization of arrays, both dense and sparse.
>
> The current "dense" format is not expressive enough to distinguish between
> an element that is not defined and one that has the value "undefined",
> but in this CL the existing behaviour of Blink is used for such cases.
> Format changes to fix these issues could be made later on.
>
> Not included in this CL is compatibility with version 0 arrays.
> Those will be implemented in a separate CL.
>
> BUG=chromium:148757
>
> Committed: https://crrev.com/2e000127df2e88e31d352ef70af397741d1f2298
> Cr-Commit-Position: refs/heads/master@{#38729}

TBR=jkummerow@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:148757

Review-Url: https://codereview.chromium.org/2255313002
Cr-Commit-Position: refs/heads/master@{#38730}