code: private boolean deleteFile(String filename) throws Exception {
          if (filename == null) {
              return false;
          }
          File file = new File(storeDir, filename);
          return Files.deleteIfExists(file.toPath());
      }
docs: Delete the file associated with a session
  
  @param filename name of the file containing the session's information
  @return true if file was deleted, false otherwise
  @throws Exception if the file associated with the session fails to be deleted