Some things like these have to be removed via Purge Unused. If it is used anywhere in your project you will not be able to purge it. Also, Revit needs some of them as prototypes from which others are designed. If you run into the situation where it is not used anywhere in your project and it still cannot be removed, try re-defining it as a viewport title you do want to use in your project, assign this to the viewports you are using in your project, then try purging the other viewport title you no longer need.
yes the purge will work but don't use the purge all button as you would in Autocad.
Also system families can be delete under the family tree. For example go to walls en there you will see the walls in the project. Right click on the wall you want to delete and see which options you get.