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

@@ -1093,17 +1093,6 @@ The ``RELEASE`` variant should be listed first in the property
 so that that variant is chosen if the user uses a configuration which is
 not an exact match for any listed ``IMPORTED_CONFIGURATIONS``.
 
-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.