Remove external_memory_accounted_in_global_limit from testing config

Bug: 361124432
Change-Id: I502c61691af999da8d614020f2b98c7616255006
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7717753
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Victor Vianna <victorvianna@google.com>
Cr-Commit-Position: refs/heads/main@{#1608502}
NOKEYCHECK=True
GitOrigin-RevId: 99e25ccb835e5a4b69664be146d986a30d441a19