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/osx/core/dcmemory.cpp

@@ -58,8 +58,7 @@ wxMemoryDCImpl::~wxMemoryDCImpl()
     if ( m_selected.Ok() )
     {
         m_selected.EndRawAccess() ;
-        delete m_graphicContext ;
-        m_graphicContext = NULL ;
+        wxDELETE(m_graphicContext);
     }
 }
 
@@ -68,8 +67,7 @@ void wxMemoryDCImpl::DoSelect( const wxBitmap& bitmap )
     if ( m_selected.Ok() )
     {
         m_selected.EndRawAccess() ;
-        delete m_graphicContext ;
-        m_graphicContext = NULL ;
+        wxDELETE(m_graphicContext);
     }
 
     m_selected = bitmap;