This dialog box lists all the Nets to which the tracks correspond. Selecting a net removes all traces corresponding to it.
To select all the net click on the 
button.
To deselect all the net click on the 
button.
To select all the nets of a class, select the class and click the Enable class button. To deselect all the nets of a class, select the class and click the Disable class button.
To remove only the added tracks from the autorouter while keeping all those tracked by manual routing, activate the Remove only objects automatically routed option.