This reverts commit 84c2dfce.

Reason for revert:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20nosnap%20-%20debug/builds/14876

Original change's description:
> Remove weak-list of optimized JS functions.
> 
> This CL removes the weak-list of JS functions from the context
> and all the code that iterares over it. This list was being used
> mainly during deoptimization (for code unlinking) and during
> garbage collection. Removing it will improve performance of
> programs that create many closures and trigger many scavenge GC
> cycles.
> 
> No extra work is required during garbage collection. However,
> given that we no longer unlink code from JS functions during
> deoptimization, we leave it as it is, and on its next activation
> we check whether the mark_for_deoptimization bit of that code is
> set, and if it is, than we unlink it and jump to lazy compiled
> code. This check happens in the prologue of every code object.
> 
> We needed to change/remove the cctests that used to check
> something on this list.
> 
> Working in x64, ia32, arm64, arm, mips64 and mips. 
> 
> Bug: v8:6637
> Change-Id: I7f192652c8034b16a9ea71303fa8e78cda3c48f3
> Reviewed-on: https://chromium-review.googlesource.com/600427
> Commit-Queue: Juliana Patricia Vicente Franco <jupvfranco@google.com>
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#47790}

TBR=mstarzinger@chromium.org,jarin@chromium.org,leszeks@chromium.org,bmeurer@chromium.org,jupvfranco@google.com

Change-Id: Ia4f1a8acf6ca5cd5c74266437a03d854b3739af2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6637
Reviewed-on: https://chromium-review.googlesource.com/647540Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47792}