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/generic/dirctrlg.cpp

@@ -1496,11 +1496,7 @@ public:
     bool OnInit() { wxTheFileIconsTable = new wxFileIconsTable; return true; }
     void OnExit()
     {
-        if (wxTheFileIconsTable)
-        {
-            delete wxTheFileIconsTable;
-            wxTheFileIconsTable = NULL;
-        }
+        wxDELETE(wxTheFileIconsTable);
     }
 };