dpkg -l | grep map
will give you the packages that most probably are related to nokia maps
browse the list carefully (some other package could have 'map' in its name and shouldn't be zapped)
then apt-get purge package-names (as root).

If you can live with having the packages still installed and you only want to get rid of the icon, you can rename the nokia-maps.desktop file in /usr/share/applications/hildon to another name, like nokia-maps.desktop.deactivated.