Use wxDELETE() and wxDELETEA() when possible.

Use wxDELETE[A]() functions which automatically NULL out their arguments after
deleting them instead of doing it manually.

Closes #9685.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64656 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/appcmn.cpp

@@ -128,8 +128,7 @@ void wxAppBase::CleanUp()
 
     wxDeleteStockLists();
 
-    delete wxTheColourDatabase;
-    wxTheColourDatabase = NULL;
+    wxDELETE(wxTheColourDatabase);
 
     wxAppConsole::CleanUp();
 }