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All the ARM linux builders already specify this, and
armhf is the now the default for both Ubuntu and Debian.

Followup cleanup cl for the bots:
https://codereview.chromium.org/1141643004/

BUG=308256

Review URL: https://codereview.chromium.org/1140503004

Cr-Commit-Position: refs/heads/master@{#330316}