code: public void clearACL(String path, String... principalNames) throws RepositoryException {
  
          final Session session = this.getAdminSession();
          final AccessControlManager acm = session.getAccessControlManager();
          final AccessControlList acl = this.getAccessControlList(session, path);
  
          final String[] principals;
          if (principalNames.length == 0) {
              // remove all existing entries
              principals = new String[] { ANY_WILDCARD };
          } else {
              principals = principalNames;
          }
  
          for (String username : principals) {
              this.removeAccessControlEntries(acl, username);
          }
  
          // the policy must be re-set
          acm.setPolicy(path, acl);
  
          session.save();
      }
docs: Removes all ACLs on the node specified by the path.
  
  @param path
  the absolute path to the node
  @param principalNames
  the user(s) whose ACL entries should be removed. If none is provided, all ACLs will be removed. A word
  of warning, if you invoke this on the root node '/' all ACls including those for administrators
  and everyone-principal will be removed, rendering the entire repository useless.