use the selector tool and choose the object, and hit backspace is an easy way. Or you can press undo to undo your last edit. I still don't know how to remove rooms, I assume they won't effect anything if you don't have a warp to them.
I am having the same issue on my mac, where I can't delete objects.  There is no backspace key on mac, just delete and fn+delete, neither of which work.  Does anyone know how to do this on mac?
For the record. You can also use `D` to delete. I find it easier, as my finger is already on S for selecting the object.
[I do agree the Delete button should have worked but doesn't. That was the first key I tried to use for deleting].