Revert "Disable data saver proxy if the warmup URL fetch fails"

This reverts commit 34a83025d52873f9ab05bb86c22479627a90bfcb.

Reason for revert: Speculative revert for crbug.com/792841

Original change's description:
> Disable data saver proxy if the warmup URL fetch fails
> 
> If the fetch of the warmup URL (aka probe URL) fails, the
> corresponding proxy is disabled, and the config is reloaded.
> 
> A future CL will add retries -- If the fetch of the probe URL
> due to network flakiness fails, then the probe will be retried
> (up to 3 times) on the same proxy.
> 
> Bug: 760294
> Change-Id: Ib255f8178ef106f5e2882ad3dc32bde143c40a90
> Reviewed-on: https://chromium-review.googlesource.com/807592
> Reviewed-by: Steven Holte <holte@chromium.org>
> Reviewed-by: Doug Arnett <dougarnett@chromium.org>
> Commit-Queue: Tarun Bansal <tbansal@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#521951}

TBR=holte@chromium.org,tbansal@chromium.org,dougarnett@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 760294, 792841
Change-Id: I804763df69665a5e3af13acdae9906c0a847cd3d
Reviewed-on: https://chromium-review.googlesource.com/817600
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522913}
11 files changed