Help: Restore documentation placeholder for removed modules

In commit cb28d9af1f (UseJava: Move helper scripts to subdirectory,
2020-11-12) we removed modules that were not meant to be documented
publicly.  In order to keep links from older versions on `cmake.org` to
the "latest" documentation working for those modules, add placeholder
documents describing the change.

Help/manual/cmake-modules.7.rst

@@ -280,6 +280,8 @@ Deprecated Utility Modules
    /module/CMakeParseArguments
    /module/MacroAddFileDependencies
    /module/TestCXXAcceptsFlag
+   /module/UseJavaClassFilelist
+   /module/UseJavaSymlinks
    /module/UsePkgConfig
    /module/Use_wxWindows
    /module/WriteBasicConfigVersionFile

Help/module/UseJavaClassFilelist.rst

@@ -0,0 +1,6 @@
+UseJavaClassFilelist
+--------------------
+
+.. versionchanged:: 3.20
+  This module was previously documented by mistake and was never meant for
+  direct inclusion by project code.  See the :module:`UseJava` module.

Help/module/UseJavaSymlinks.rst

@@ -0,0 +1,6 @@
+UseJavaSymlinks
+---------------
+
+.. versionchanged:: 3.20
+  This module was previously documented by mistake and was never meant for
+  direct inclusion by project code.  See the :module:`UseJava` module.