I believe it's in a file called HISTORY.DAT in:-
Don't know what will happen if you delete it......so try moving it.
Perhaps MM will renew it.
EDIT: Just tried deleting this and the info is still displayed....perhaps you can't clear it ??
Car : Ford Focus Zetec S 1800cc
Carpc :Galaxy GT-P1000 Original 7in Tab
Mounted in "On Dash" Custom Install
If you select the menu option to navigate to favourites (or "favorites" if you prefer ), highlight each destination item, then the red "Tools" button at the top - one of the options is edit, or you can delete it.
You will need to do this for each item in your favourites list - I don't know a way to do them all at the same time.
The same thing works for removing items from the history list, or any of the other lists (eg "Roadworks")