Clean up after jenkinsci/jenkins#9150

Author: basil

src/main/java/com/cloudbees/hudson/plugins/folder/AbstractFolderDescriptor.java

@@ -39,10 +39,6 @@
 import jenkins.model.Jenkins;
 import jenkins.model.ProjectNamingStrategy;
 import org.jenkins.ui.icon.IconSpec;
-import org.kohsuke.accmod.Restricted;
-import org.kohsuke.accmod.restrictions.NoExternalUse;
-import org.kohsuke.stapler.AncestorInPath;
-import org.kohsuke.stapler.QueryParameter;
 import org.kohsuke.stapler.Stapler;
 import org.kohsuke.stapler.StaplerRequest2;
 
@@ -134,12 +130,6 @@ public List<FolderIconDescriptor> getIconDescriptors() {
         return r;
     }
 
-    @Restricted(NoExternalUse.class)
-    public FormValidation doCheckDisplayNameOrNull(@AncestorInPath AbstractFolder folder, @QueryParameter String value) {
-        return Jenkins.get().doCheckDisplayName(value, folder.getName());
-    }
-
-
     /**
      * Needed if it wants Folder are categorized in Jenkins 2.x.
      *