See https://github.com/OctopusDeploy/Issues/issues/3169 for our plan and a workaround to get you started right now!
The dashboard no longer shows the untenanted deployments. However, the project overview still does. We don't want to delete these deployments are they are key parts of the projects history.
In saying that, they are confusing to look at as of today since we now follow the multi-tentanted deployment process and untenanted deployments are dead to us now.
We have untenanted deployments still showing on the project overview going back as far as July 2016.