Remove WPT failure expectations for (now enabled by default) CORB.

The failure expectations for some wpt/fetch/corb/*tentative* tests were
only needed while CORB was still disabled by default.  These test
expectations can be removed now, because CORB is enabled by default
since r553830.

Bug: 802835
Change-Id: If09646e3cfec268e2a9ec72aa870d8fa2a4460e3
Reviewed-on: https://chromium-review.googlesource.com/1030612
Reviewed-by: Charlie Reis <creis@chromium.org>
Commit-Queue: Ɓukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554192}
4 files changed