Remove testRunner references in wpt tests

These references have no effect, so remove them.

Bug: 761391
Change-Id: I85df5d4520f9d6b4719c86a903a22360df3ae421
Reviewed-on: https://chromium-review.googlesource.com/665338


Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505666}