Fix render [:] as JSON crash in deleteOrganismFeatures

The inline map literal [:] in render [:] as JSON causes a
MissingPropertyException when executed inside the transactional template
generated by the class-level @transactional annotation. Use a JSONObject
variable instead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: cmdcolin

grails-app/controllers/org/bbop/apollo/OrganismController.groovy

@@ -200,7 +200,8 @@ class OrganismController {
         log.info "Deleted ${deleted} features for organism ${organism.commonName}"
       }
 
-      render [:] as JSON
+      def result = new JSONObject()
+      render result as JSON
     }
     catch (Exception e) {
       def error = [error: 'problem removing organism features for organism: ' + e]