DevTools: ConsoleViewMessage is not targetaware

ConsoleViewMessage wraps consoleMessage model object which is already
TargetAware - no need to extend WebInspector.TargetAware here.

Review URL: https://codereview.chromium.org/251273002

git-svn-id: svn://svn.chromium.org/blink/trunk@172859 bbb929c8-8fbe-4397-9dbb-9b2b20218538