Delete the button object in wxRibbonButtonBar::DeleteButton().

Unlike ClearButtons(), DeleteButton() didn't actually delete the button.

Fix this and document this behaviour.

Closes #15909.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75710 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/ribbon/buttonbar.h

@@ -442,7 +442,10 @@ public:
     
     /**
         Delete a single button from the button bar.
-        
+
+        The corresponding button is deleted by this function, so any pointers to
+        it previously obtained by GetItem() or GetItemById() become invalid.
+
         @see ClearButtons()
     */
     virtual bool DeleteButton(int button_id);