Revert of [chromedriver] Set mobile=true when calling setDeviceMetricsOverride (patchset #1 id:1 of https://codereview.chromium.org/668783002/)

Reason for revert:
This is breaking mobile emulation tests (testDeviceMetrics and testDeviceName). For some reason, window.innerHeight/innerWidth get reported incorrectly when this patch is applied.

Original issue's description:
> [chromedriver] Set mobile=true when calling setDeviceMetricsOverride
>
> BUG=chromedriver:944
> TBR=stgao@chromium.org
>
> Committed: https://crrev.com/02d008b0ee86ef7037833d27cf92b45f9125f097
> Cr-Commit-Position: refs/heads/master@{#300390}

TBR=srawlins@google.com,stgao@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=chromedriver:944

Review URL: https://codereview.chromium.org/666173002

Cr-Commit-Position: refs/heads/master@{#300494}