Remove the test which prevented the generation of erase background events from
wxMSW::wxWindow::HandleEraseBkgnd(). Although it is true that native controls
mostly erase background on their own, there are exceptions: we must erase the
background of wxToolBar ourselves, for example. More importantly, there is no
reason to prevent the user code from defining wxEVT_ERASE_BACKGROUND handlers
for the native controls as this works just fine under MSW (although it doesn't
under GTK nor probably other ports...). So also add a test erase background
handler to the toolbar sample to verify that this does work.
Closes#11514.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62805 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
0639363014