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

samples/fswatcher/fswatcher.cpp

@@ -279,8 +279,7 @@ void MyFrame::OnWatch(wxCommandEvent& event)
     {
         wxCHECK_RET(m_watcher, "Watcher not initialized");
         m_filesList->DeleteAllItems();
-        delete m_watcher;
-        m_watcher = NULL;
+        wxDELETE(m_watcher);
     }
 }