Remove @need_sphinx from test_slots.py

Now that the `test` dependency group includes `docs`, the mark does nothing.

Thanks @webknjaz

Author: clayote

tests/test_slots.py

@@ -778,12 +778,6 @@ def documented(self):
         return True
 
 
-need_sphinx = pytest.mark.skipif(
-    Sphinx is None, reason="Sphinx is not installed"
-)
-
-
-@need_sphinx
 def test_sphinx_autodocuments_cached_property():
     """
     Sphinx can generate autodocs for cached properties in slots classes
@@ -809,7 +803,6 @@ def test_sphinx_autodocuments_cached_property():
             assert written.read() == good.read()
 
 
-@need_sphinx
 def test_sphinx_automembers_cached_property():
     """
     Sphinx can find cached properties in the :members: of slots classes