On the Tools menu, click "Merge walls on delete". This option also exists on the Create New Floor dialog for "Copy perimeter walls from selected floor" and "Copy perimeter walls with offset".
Where two walls meet at a junction, a "wall divide" will be introduced. Wall divides can be highlighted using the "Select End" tool. Wall divides can also be added manually with the "Divide Wall" option on the Create toolbar. In this instance there isn't a junction, as the divide exists on a section of wall without an intersecting wall.
Provided the same building element exists either side of the junction, the wall divide is automatically removed when the intersecting wall is deleted. This is true when "Merge walls on delete" is selected on the Tools menu. Otherwise the wall divide will remain in-situ after the adjoining wall has been deleted.