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It's currently set to false by default and there's no bot setting it.
It was used in manual testing but hasn't been used for a long time.
This CL removes this gn arg.

Bug: 1067786
Change-Id: Idf7c57898f335b10441eb32e1509b2bee25c5368
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2136310Reviewed-by: Yuchen Liu <yucliu@chromium.org>
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756498}