Remove a WebVTT newlines test that doesn't do what it says

tc003-newlines.vtt had CR line endings, not mixed as the test claimed.

Mixed line endings are sufficiently covered by
media/track/opera/track/webvtt/parsing/support/newlines.vtt

BUG=318734

Review URL: https://codereview.chromium.org/65493006

git-svn-id: svn://svn.chromium.org/blink/trunk@162024 bbb929c8-8fbe-4397-9dbb-9b2b20218538