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/dmc.rsp

@@ -176,8 +176,6 @@ samples/sashtest/makefile.dmc
 samples/sashtest/makefile.dms
 samples/scroll/makefile.dmc
 samples/scroll/makefile.dms
-samples/scrollsub/makefile.dmc
-samples/scrollsub/makefile.dms
 samples/shaped/makefile.dmc
 samples/shaped/makefile.dms
 samples/sockets/makefile.dmc