Remove references to WithSource in the docs

Refs #2350.

master/docs/manual/cfg-properties.rst

@@ -266,48 +266,3 @@ above cannot contain more substitutions.
 Note: like python, you can use either positional interpolation *or*
 dictionary-style interpolation, not both. Thus you cannot use a string like
 ``WithProperties("foo-%(revision)s-%s", "branch")``.
-
-.. Index:: single; Properties; WithSource
-
-.. _WithSource:
-
-WithSource
-++++++++++
-
-A build may contain more than one sourcestamp. Buildsteps may need information 
-from a sourcestamp like repository or branch to be able to perform their task.
-The class :class:`WithSource` interpolates the atrributes from a single sourcestamp
-into a string that can be used by a buildstep. 
-
-The simplest use of this class is with positional string interpolation.  Here,
-``%s`` is used as a placeholder, and attribute names are given as subsequent
-arguments::
-
-    from buildbot.steps.shell import ShellCommand
-    from buildbot.process.properties import WithSource
-    f.addStep(ShellCommand(
-              command=["tar", "czf",
-                       WithSource("mailexe","mailer-%s-%s.tar.gz", "branch", "revision"),
-                       "source"]))
-    
-In this example 'mailexe' is the codebase for the mail application. Branch and revision
-are the attibute names inside the sourcestamp that belongs to the application.
-
-.. index:: unsupported format character
-
-The more common pattern is to use python dictionary-style string interpolation
-by using the ``%(propname)s`` syntax. In this form, the property name goes in
-the parentheses, as above.  A common mistake is to omit the trailing "s",
-leading to a rather obscure error from Python ("ValueError: unsupported format
-character")::
-
-   from buildbot.steps.shell import ShellCommand
-   from buildbot.process.properties import WithSource
-   f.addStep(ShellCommand(command=[ 'make', WithSource('mailexe','REVISION=%(revision)s'),
-                                    'dist' ]))
-
-This example will result in a ``make`` command with an argument like
-``REVISION=12098``.
-
-The :ref:`dictionary style<WithProperties-DictStyle>` interpolation supports a number of more advanced
-syntaxes in the parentheses.