Remove pure flicker app from VR motopho test

Removes the URL for the pure flicker app from the list of test URLs for
the VR motion to photon latency test. This is due to several reasons:

1. The page is pretty redundant at this point. The WebVR samples have
    flicker app capabilities built in now, and give almost identical
    results as long as the CPU/GPU load isn't cranked up.
2. The URL seems to have died, which was causing the test to fail
3. This makes all the test URLs come from the WebVR sample repo, which
    makes it easier to control versions for testing.

Bug: 
Change-Id: Ibcf5a720842314354e0dfe44af73edc41c77398b
Reviewed-on: https://chromium-review.googlesource.com/849274Reviewed-by: Christopher Grant <cjgrant@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527042}

chrome/test/vr/perf/latency/webvr_latency_test.py

@@ -20,12 +20,6 @@ MOTOPHO_THREAD_TIMEOUT = 15
 MOTOPHO_THREAD_TERMINATION_TIMEOUT = 2
 MOTOPHO_THREAD_RETRIES = 4
 DEFAULT_URLS = [
-    # TODO(bsheedy): See about having versioned copies of the flicker app
-    # instead of using personal github.
-    # Purely a flicker app - no additional CPU/GPU load.
-    'https://weableandbob.github.io/Motopho/'
-    'flicker_apps/webvr/webvr-flicker-app-klaus.html?'
-    'polyfill=0\&canvasClickPresents=1',
     # URLs that render 3D scenes in addition to the Motopho patch.
     # Heavy CPU load, moderate GPU load.
     'https://webvr.info/samples/test-slow-render.html?'