This reverts commit c5ad9c6d.

Reason for revert: Fails on gc stress:
https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20GC%20Stress%20-%20custom%20snapshot/builds/12661

Original change's description:
> [TypeFeedbackVector] Store optimized code in the vector
> 
> Since the feedback vector is itself a native context structure, why
> not store optimized code for a function in there rather than in
> a map from native context to code? This allows us to get rid of
> the optimized code map in the SharedFunctionInfo, saving a pointer,
> and making lookup of any optimized code quicker.
> 
> Original patch by Michael Stanton <mvstanton@chromium.org>
> 
> BUG=v8:6246
> 
> Change-Id: I60ff8c408c3001bc272b4b198c9cbaea2872a9e5
> Reviewed-on: https://chromium-review.googlesource.com/476891
> Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
> Reviewed-by: Michael Stanton <mvstanton@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#45022}

TBR=ulan@chromium.org,rmcilroy@chromium.org,yangguo@chromium.org,mvstanton@chromium.org,jarin@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:6246

Change-Id: I9cd5735b03898cae6ae7adea0f19d32fceb31619
Reviewed-on: https://chromium-review.googlesource.com/493287Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45027}