Removes obsolete test harness expectations

run_blink_tests.py complains when an all-pass testharness test
has expectations. For example:

external/wpt/css/css-transitions/CSSTransition-startTime.tentative.html
is a all-pass testharness test, but has an extra baseline file.
Please remove CSSTransition-startTime.tentative-expected.txt

These warnings are annoying when running tests locally.

Could we modify our test linter to treat blank expectations
for testharness tests as an error?

I've did a similar cleanup on Jan 30th, in
https://chromium-review.googlesource.com/c/chromium/src/+/1447255

Bug: 726520
Change-Id: I9027526824841874c8a692e23c9f6ff6119a5576
Reviewed-on: https://chromium-review.googlesource.com/c/1479420
Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Aleks Totic <atotic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633906}
16 files changed