Help: Drop FeatureSummary example in cmake-developer.7

The use of FeatureSummary inside a find module is not a convention
yet used by upstream CMake modules.  Drop the example from the
documentation about how to write find modules.  If in the future
we add use of FeatureSummary to many of the upstream find modules
then this example can be restored as part of establishing the
convention.

Help/manual/cmake-developer.7.rst

@@ -1115,17 +1115,6 @@ not any of its dependencies.  Instead, those dependencies should also be
 targets, and CMake should be told that they are dependencies of this target.
 CMake will then combine all the necessary information automatically.
 
-We should also provide some information about the package, such as where to
-download it.
-
-.. code-block:: cmake
-
-  include(FeatureSummary)
-  set_package_properties(Foo PROPERTIES
-    URL "http://www.foo.example.com/"
-    DESCRIPTION "A library for doing useful things"
-  )
-
 Most of the cache variables should be hidden in the ``ccmake`` interface unless
 the user explicitly asks to edit them.