It is very easy to delete schemas from Cloudera Schema Registry if you need to do so. I recommend downloading them and having a backup first.
Let's look at our schema
Well let's get rid of that junk.
Here is the documentation For CDF Datahub in CDP Public Cloud
curl -X DELETE "http://MYSERVERHASACOOLNAME.DEV:7788/api/v1/schemaregistry/schemas/ junk" -H "accept: application/json"
Where junk is the name of my schema.
You could call this REST API from NiFi, a DevOps tool or just a simple CURL like listed above.
Knox and other security may apply.