Remove xfail marker from passing tests (#994)

test_augassign_recursion has been passing for a while. The remaining
tests were fixed by context.path changes in 15e1921.

tests/unittest_inference.py

@@ -1229,7 +1229,6 @@ def __init__(self):
         self.assertEqual(len(foo_class.instance_attrs["attr"]), 1)
         self.assertEqual(bar_class.instance_attrs, {"attr": [assattr]})
 
-    @pytest.mark.xfail(reason="Relying on path copy")
     def test_nonregr_multi_referential_addition(self):
         """Regression test for https://github.com/PyCQA/astroid/issues/483
         Make sure issue where referring to the same variable
@@ -1243,7 +1242,6 @@ def test_nonregr_multi_referential_addition(self):
         variable_a = extract_node(code)
         self.assertEqual(variable_a.inferred()[0].value, 2)
 
-    @pytest.mark.xfail(reason="Relying on path copy")
     def test_nonregr_layed_dictunpack(self):
         """Regression test for https://github.com/PyCQA/astroid/issues/483
         Make sure multiple dictunpack references are inferable
@@ -2329,7 +2327,6 @@ def no_yield_mgr():
         self.assertRaises(InferenceError, next, module["other_decorators"].infer())
         self.assertRaises(InferenceError, next, module["no_yield"].infer())
 
-    @pytest.mark.xfail(reason="Relying on path copy")
     def test_nested_contextmanager(self):
         """Make sure contextmanager works with nested functions
 
@@ -4890,7 +4887,6 @@ class instance(object):
         self.assertIsInstance(inferred, Instance)
 
 
-@pytest.mark.xfail(reason="Relying on path copy")
 def test_augassign_recursion():
     """Make sure inference doesn't throw a RecursionError
 

tests/unittest_object_model.py

@@ -358,7 +358,6 @@ def test(self): return 42
             with self.assertRaises(exceptions.InferenceError):
                 next(node.infer())
 
-    @pytest.mark.xfail(reason="Relying on path copy")
     def test_descriptor_error_regression(self):
         """Make sure the following code does
         node cause an exception"""