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Revert of Implement arflags in the GN build. (patchset #2 id:20001 of https://codereview.chromium.org/1896163003/ )

Reason for revert:
variety of compile failures on Android bots that have been switched to GN, see https://codereview.chromium.org/1896163003/#msg18

Original issue's description:
> Implement arflags in the GN build.
>
> This flag was recently added in GN. This patch hooks it up to the toolchains
> and moves some flags to use it that previously had to be hardcoded on the
> tool command itself.
>
> Remove concurrent_links variable from gcc_toolchain which was unused.
>
> BUG=598599

TBR=brucedawson@chromium.org,brettw@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=598599

Review URL: https://codereview.chromium.org/1903363003

Cr-Commit-Position: refs/heads/master@{#388646}