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}