Execution example::

  config_delete nonexistent
  # [
  #   [
  #     -22, 
  #     1337566253.89858, 
  #     0.000355720520019531, 
  #     "[config][delete] failed to delete", 
  #     [
  #       [
  #         "grn_config_delete", 
  #         "config.c", 
  #         166
  #       ]
  #     ]
  #   ], 
  #   false
  # ]
