Deprecate WebUI-based connectivity diagnostics.

This is replaced with the packaged connectivity diagnostics app.

BUG=277741
TEST=trybots
R=thestig@chromium.org, zork@chromium.org

Review URL: https://codereview.chromium.org/68103006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234351 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234351