No reason to expected ufunc.types_ to be None.

Example where that assumption is wrong is the following test invocation:

```
python -m pytest \
   dpctl/tests/test_tensor_*.py \
   dpctl/tests/test_usm_ndarray_*.py \
   dpctl/tests/elementwise/test_a*.py
```

Removed test of `uf.types_` to be `None` altogether per PR feedback.

Author: oleksandr-pavlyk

dpctl/tests/elementwise/test_abs.py

@@ -70,10 +70,8 @@ def test_abs_usm_type(usm_type):
     assert np.allclose(dpt.asnumpy(Y), expected_Y)
 
 
-def test_abs_types_prop():
+def test_abs_types_property():
     get_queue_or_skip()
-    types = dpt.abs.types_
-    assert types is None
     types = dpt.abs.types
     assert isinstance(types, list)
     assert len(types) > 0

dpctl/tests/elementwise/test_add.py

@@ -260,8 +260,6 @@ def __sycl_usm_array_interface__(self):
 
 def test_add_types_property():
     get_queue_or_skip()
-    types = dpt.add.types_
-    assert types is None
     types = dpt.add.types
     assert isinstance(types, list)
     assert len(types) > 0