Delete PPAPI testing code

Bug: 40511450
Change-Id: Ia9dde260b1dfe9d9e2273cb5e5326ebac4ce7bac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6670296
Reviewed-by: Fabian Sommer <fabiansommer@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1478595}
NOKEYCHECK=True
GitOrigin-RevId: 6420f71a85eb194385f757036ab2c84d0ff831cc