swarming: remove depreacated flag from swarming
swarming: remove depreacated flag from swarming

The flag is no-op, and I removed code using that.

Bug: 997221
Change-Id: I7eefc986603cc4d8a9ee9b760d9501b3b8ce6d71
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2029350
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Yoshisato Yanagisawa <5d95c5c75e3d691d9c77888fff4498e04f8b7157@google.com>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>

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