Help: Move cmake_path release note from 3.19 to post-3.19 development

The feature has been removed from the 3.19 branch, but has been kept in
post-3.19 development.  Move the release note accordingly.

Help/release/3.19.rst

@@ -87,9 +87,6 @@ Commands
 * The :command:`cmake_language` command gained a ``DEFER`` mode to
   schedule command calls to occur at the end of processing a directory.
 
-* The :command:`cmake_path` command was added for operations on
-  filesystem paths.
-
 * The :command:`configure_file` command gained a ``NO_SOURCE_PERMISSIONS``
   option to suppress copying the input file's permissions to the output file.
 

Help/release/dev/cmake_path.rst

+cmake_path
+----------
+
+* The :command:`cmake_path` command was added for operations on
+  filesystem paths.