Help: Drop development topic notes to prepare release

Release versions do not have the development topic section of
the CMake Release Notes index page.

Help/release/dev/0-sample-topic.rst

-0-sample-topic
---------------
-
-* This is a sample release note for the change in a topic.
-  Developers should add similar notes for each topic branch
-  making a noteworthy change.  Each document should be named
-  and titled to match the topic name to avoid merge conflicts.

Help/release/index.rst

@@ -5,8 +5,6 @@ CMake Release Notes
   This file should include the adjacent "dev.txt" file
   in development versions but not in release versions.
 
-.. include:: dev.txt
-
 Releases
 ========