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/msw/statbmp.cpp

@@ -239,9 +239,7 @@ wxBitmap wxStaticBitmap::GetBitmap() const
 
 void wxStaticBitmap::Free()
 {
-    delete m_image;
-
-    m_image = NULL;
+    wxDELETE(m_image);
 }
 
 wxSize wxStaticBitmap::DoGetBestSize() const