bpo-23984: Improve descriptor documentation (GH-1034)

https://bugs.python.org/issue23984

Doc/howto/descriptor.rst

@@ -372,9 +372,9 @@ calls are unexciting::
     ...         print(x)
     ...     f = staticmethod(f)
     ...
-    >>> print(E.f(3))
+    >>> E.f(3)
     3
-    >>> print(E().f(3))
+    >>> E().f(3)
     3
 
 Using the non-data descriptor protocol, a pure Python version of