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/widgets/gauge.cpp

@@ -335,8 +335,7 @@ void GaugeWidgetsPage::StopTimer(wxButton *clicked)
     wxCHECK_RET( m_timer, wxT("shouldn't be called") );
 
     m_timer->Stop();
-    delete m_timer;
-    m_timer = NULL;
+    wxDELETE(m_timer);
 
     if (clicked->GetId() == GaugePage_Progress)
     {