Remove newly-failing aura-specific test suites from Win8 Aura bot config.

Remove newly-failing aura-specific test suites from Win8 Aura bot config.

We've flipped Win8 Aura from GYP to GN, and the following test
suites are failing badly:

  ash_unittests
  aura_unittests
  compositor_unittests
  views_unittests
  wm_unittests

We did not have test coverage for these (or any) steps on the GN
bots previously, so they may just be flat-out broken. I will
disable these tests for now, and we can triage and add them back in
once the bot is green. At least some test suites are passing,
so the bot isn't completely broken.

TBR=scottmg@chromium.org
BUG=497423
NOTRY=true

Review URL: https://codereview.chromium.org/1163393003

Cr-Commit-Position: refs/heads/master@{#333402}