[Most Visited] Removing Most Visited Tiles experiment code, which is obsolete.

      Experiment is no longer running and is in many ways obsolete. Removing the code.

BUG=None
TEST=manual

Review URL: https://codereview.chromium.org/437803003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287624 0039d316-1c4b-4281-b951-d872f2087c98