[Trivial] Remove console.log spam from flakiness_dashboard.js

This patch removes a console.log from the flakiness dashboard that
would write the number of tests to the console.

Review URL: https://codereview.chromium.org/389183002

git-svn-id: svn://svn.chromium.org/blink/trunk@178015 bbb929c8-8fbe-4397-9dbb-9b2b20218538