Here is how I get rid of them(for a while at least) on my WinXP system. [I haven't found the part of the Iron scripts that store the damned things!]
Get a copy of a good lite database browser. I use SQLite Database Browser 1.3 (There may be better ones, I don't know)http://www.medownloads.com/download-SQLite-Database-Browser-72353.htm
Then go to your Iron profile >> C:\Documents and Settings\Bill\Local Settings\Application Data\Chromium\User Data\Iron6\Default
and open the 'History' file with the database browser.
Then using the 'Browse Data' tab, and the drop down, go the to 'urls' section. (off to the right you will see the favicon_id column).
I just click the REMOVE RECORD button, and the next time I open Iron the favicons are gone. They do tend to show back up, and someday I will find how they are store, and tell Iron to STOP IT!