DevTools: Minor clean-up to delete obsolete code.

This is a follow-up to https://codereview.chromium.org/17024003
Tested by existing test.

BUG=249655
R=yurys@chromium.org

Review URL: https://codereview.chromium.org/64603002

git-svn-id: svn://svn.chromium.org/blink/trunk@161550 bbb929c8-8fbe-4397-9dbb-9b2b20218538