Revert of [turbofan] Discard the shared code entry in the optimized code map. (patchset #3 id:40001 of https://codereview.chromium.org/2401653002/ )

Reason for revert:
Possible GCSTRESS failure, investigating.

Original issue's description:
> [turbofan] Discard the shared code entry in the optimized code map.
>
> At one time, we hoped to generate the same code for different
> native contexts. But in truth, much performance comes from optimizing
> on the native context. Now we abandon this pathway.
>
> BUG=
>
> Committed: https://crrev.com/55af3c44c99a6e4cd6d53df775023d760ad2b2c3
> Cr-Commit-Position: refs/heads/master@{#40079}

TBR=mstarzinger@chromium.org,ishell@chromium.org,bmeurer@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review-Url: https://codereview.chromium.org/2403453002
Cr-Commit-Position: refs/heads/master@{#40081}