Disable WebChecks in presubmit.
Disable WebChecks in presubmit.

This uses unpinned external dependencies, and so has started breaking
without any commits to this repo :(.

R=nodir@chromium.org, 9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org

Bug: 794670
Change-Id: I53ffd3cfd14c7d002e51844443e7ee4d9898e062
Reviewed-on: https://chromium-review.googlesource.com/825590
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go