Merge branch 'aui-delete-tool'

Provide work around for surprising behaviour of
wxAuiToolBar::DeleteTool().

Closes https://github.com/wxWidgets/wxWidgets/pull/1758

include/wx/aui/auibar.h

@@ -525,6 +525,12 @@ public:
 
     void ClearTools() { Clear() ; }
     void Clear();
+
+    bool DestroyTool(int toolId);
+    bool DestroyToolByIndex(int idx);
+
+    // Note that these methods do _not_ delete the associated control, if any.
+    // Use DestroyTool() or DestroyToolByIndex() if this is wanted.
     bool DeleteTool(int toolId);
     bool DeleteByIndex(int toolId);