reorganize scroll sample to make it possible to understand what it does both when reading its code and when running it; merged scrollsub sample in it and removed the original one

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@57523 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

distrib/scripts/manifests/makefile.rsp

@@ -87,7 +87,6 @@ samples/richtext/Makefile.in
 samples/rotate/Makefile.in
 samples/sashtest/Makefile.in
 samples/scroll/Makefile.in
-samples/scrollsub/Makefile.in
 samples/shaped/Makefile.in
 samples/sockets/Makefile.in
 samples/sound/Makefile.in