DevTools: Remove unused methods after migration to the overridden version

BUG=404355
R=pfeldman-OOO, yurys

Review URL: https://codereview.chromium.org/508603002

git-svn-id: svn://svn.chromium.org/blink/trunk@181018 bbb929c8-8fbe-4397-9dbb-9b2b20218538