Removed buildout.dumppickedversions from the warning.

I *have* retained buildout.dumppickedversions in the doctest with
the qualification 'only part of it'.

Removing the warning *does* make it less obvious for the people
that use buildout.dumppickedversions in the way I thought it
was used most, but apparently the default behaviour of dumppickedversions
was otherwise.

src/zc/buildout/buildout.py

@@ -953,14 +953,13 @@ class Buildout(DictMixin):
     def _load_extensions(self):
         __doing__ = 'Loading extensions.'
         specs = self['buildout'].get('extensions', '').split()
-        for superceded_extension in ['buildout-versions',
-                                     'buildout.dumppickedversions']:
-            if superceded_extension in specs:
-                msg = ("The extension %s is now included in buildout itself.\n"
-                       "Remove the extension from your configuration and "
-                       "look at the `show-picked-versions`\n"
-                       "option in buildout's documentation.")
-                raise zc.buildout.UserError(msg % superceded_extension)
+        if 'buildout-versions' in specs:
+            raise zc.buildout.UserError(
+                "The extension 'buildout-versions' is now included in "
+                "buildout itself.\n"
+                "Remove the extension from your configuration and "
+                "look at the `show-picked-versions`\n"
+                "option in buildout's documentation.")
         if specs:
             path = [self['buildout']['develop-eggs-directory']]
             if self.offline:

src/zc/buildout/repeatable.txt

@@ -408,7 +408,7 @@ The versions file contains the extra pin:
     >>> 'spam = 2' in open('my_versions.cfg').read()
     True
 
-Because buildout now includes buildout-versions' (and the older
+Because buildout now includes buildout-versions' (and part of the older
 buildout.dumppickedversions') functionality, it warns if these extensions are
 configured.
 
@@ -425,6 +425,6 @@ configured.
     While:
       Installing.
       Loading extensions.
-    Error: The extension buildout-versions is now included in buildout itself.
+    Error: The extension 'buildout-versions' is now included in buildout itself.
     Remove the extension from your configuration and look at the `show-picked-versions`
     option in buildout's documentation.