This means that one cannot disband a city to settlers in the Qt-client, as the default for that setting (that cannot be changed) is to disallow disbanding.
It actually is there - just not very discoverable.
On has to right-click on the worklist area to open a menu where it's included.
In the qt version, there is no flag to enable disband the city flag to remove city when building settler in a city with 1 population.
It's a Great game by the way; keep up the good work