code: def check_remove_unused(self):
      self.link.remove_unused()
  
      self.assertEqual(self.link.layer_names, self.layer_names)
      for name in ["l1", "f1", "f2", "l2"]:
          if name in self.layer_names:
              self.assertTrue(hasattr(self.link, name))
          else:
              self.assertFalse(hasattr(self.link, name))
  
imports: import numpy
  import unittest
  import chainer
  from chainer.backends.cuda import to_cpu
  from chainer.function import Function
  from chainer import testing
  from chainer.testing import attr
  from chainercv.links import PickableSequentialChain
  from chainercv.utils.testing import ConstantStubLink
label_desc: Use image node_id 2 for calling the TestPickableSequentialChainRemoveUnused obj's underlying member method code with example usage: obj.check_remove_unused() without return types