gh-105751: test_ctypes avoids the operator module (GH-105797)

* Replace operator.delitem(obj, index) with "del obj[index]".
* Replace operator.setitem(obj, index, value) with
  "obj[index] = value".
* Replace delattr(obj, "attr) with "del obj.attr".
* Replace grc() with sys.getrefcount() for readability.