Revert of gn: Remove unnecessary v8 defaults (patchset #7 id:120001 of https://codereview.chromium.org/2058033002/ )

Reason for revert:
Seems to have broken Google Chrome Mac builder:
/b/c/b/Google_Chrome_Mac/src/buildtools/mac/gn gen //out/Release --check
  -> returned 1
ERROR at //chrome/BUILD.gn:514:7: Replacing nonempty list.
      remove_configs = [ "//build/config/mac:strip_all" ]
      ^-------------
This overwrites a previously-defined nonempty list (length 2).
See //v8/gni/v8.gni:55:3: for previous definition
  remove_configs += [ "//build/config/compiler:default_optimization" ]
  ^------------------------------------------------------------------
with another one (length 1). Did you mean "+=" to append instead? If you
really want to do this, do
  remove_configs = []
before reassigning.
See //BUILD.gn:202:7: which caused the file to be included.
      "//chrome",
      ^---------
GN gen failed: 1

Original issue's description:
> gn: Remove unnecessary v8 defaults
>
> Remove chromium defaults for v8_optimized_debug and
> v8_use_external_startup_data.
>
> This is not needed after v8 provides these defaults:
> https://codereview.chromium.org/2025803003/
> https://codereview.chromium.org/2024833002/
>
> It also interferes if somebody tries to override the gn args
> with a different value.
>
> BUG=chromium:616034
> TBR=alokp@chromium.org, brettw@chromium.org
>
> Committed: https://crrev.com/0fffeb2adaa3c284b760922c1aecce1516b998ce
> Cr-Commit-Position: refs/heads/master@{#406067}

TBR=jochen@chromium.org,dpranke@chromium.org,vogelheim@chromium.org,alokp@chromium.org,brettw@chromium.org,machenbach@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:616034

Review-Url: https://codereview.chromium.org/2160663003
Cr-Commit-Position: refs/heads/master@{#406072}
11 files changed