I usually remove all content from a topic when I do not want it anymore. I must admit I had never thought of deleting one.
You can of course hide the topic from view using the "eye" or even move it down the list and change the number of topics (ie originally 10 increase to 11 move unwanted to 11 then reduce back to 10). This latter is rather long winded and does not actually remove the topic anyway.
Hope this helps.
Inserting a section between existing sections would be even more useful to me