DevTools: remove obsolete test-runner.html file

This patch removes obsolete test-runner.html file from DevTools front-end
folder.

TBR=pfeldman
BUG=

Review URL: https://codereview.chromium.org/163683005

git-svn-id: svn://svn.chromium.org/blink/trunk@167103 bbb929c8-8fbe-4397-9dbb-9b2b20218538