Minor cleanup in the gc module.
Removed gc.DEBUG_OBJECT: there is only one kind of objects.
Now gc.DEBUG_COLLECTABLE or gc.DEBUG_UNCOLLECTABLE can be used alone to print the
corresponding list of objects.

Also removed a footnote about version 2.2, and a comment explaining some deleted code.
diff --git a/Doc/library/gc.rst b/Doc/library/gc.rst
index 4a4dfde..99504c6 100644
--- a/Doc/library/gc.rst
+++ b/Doc/library/gc.rst
@@ -131,7 +131,7 @@
 
    A list of objects which the collector found to be unreachable but could not be
    freed (uncollectable objects).  By default, this list contains only objects with
-   :meth:`__del__` methods. [#]_ Objects that have :meth:`__del__` methods and are
+   :meth:`__del__` methods. Objects that have :meth:`__del__` methods and are
    part of a reference cycle cause the entire reference cycle to be uncollectable,
    including objects not necessarily in the cycle but reachable only from it.
    Python doesn't collect such cycles automatically because, in general, it isn't
@@ -169,18 +169,6 @@
    the ``garbage`` list.
 
 
-.. data:: DEBUG_INSTANCES
-
-   When :const:`DEBUG_COLLECTABLE` or :const:`DEBUG_UNCOLLECTABLE` is set, print
-   information about instance objects found.
-
-
-.. data:: DEBUG_OBJECTS
-
-   When :const:`DEBUG_COLLECTABLE` or :const:`DEBUG_UNCOLLECTABLE` is set, print
-   information about objects other than instance objects found.
-
-
 .. data:: DEBUG_SAVEALL
 
    When set, all unreachable objects found will be appended to *garbage* rather
@@ -191,10 +179,6 @@
 
    The debugging flags necessary for the collector to print information about a
    leaking program (equal to ``DEBUG_COLLECTABLE | DEBUG_UNCOLLECTABLE |
-   DEBUG_INSTANCES | DEBUG_OBJECTS | DEBUG_SAVEALL``).
+   DEBUG_SAVEALL``).
 
 .. rubric:: Footnotes
-
-.. [#] Prior to Python 2.2, the list contained all instance objects in unreachable
-   cycles,  not only those with :meth:`__del__` methods.
-