Revert "testing/libfuzzer: build individual_fuzztest_wrapper only in chromium"

This reverts commit cff36b35.

Reason for revert: Breaks WebRTC's tests.

https://ci.chromium.org/ui/p/webrtc/builders/try/linux_libfuzzer_rel/70175/overview

Original change's description:
> testing/libfuzzer: build individual_fuzztest_wrapper only in chromium
>
> This is to fix `gn gen` failure in the testing roll CL to dawn.
> e.g.
> https://logs.chromium.org/logs/dawn/buildbucket/cr-buildbucket/8745995919527078337/+/u/gn_gen__2_/stdout
>
> Bug: 341220050
> Change-Id: If4525ed12b75a71d38656060aa2a8df3d55450ab
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5601256


> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
> Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
> Reviewed-by: Adrian Taylor <adetaylor@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1311728}

Bug: 341220050, b/345708910
Change-Id: I41f199c9b237f57a944cbea3343a520fcef1b949
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5604244


Commit-Queue: Adrian Taylor <adetaylor@chromium.org>
Reviewed-by: Adrian Taylor <adetaylor@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Adrian Taylor <adetaylor@google.com>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312688}