Remove a warning from a comment and update NEWS.

taglib/asf/asffile.h

@@ -112,9 +112,6 @@ namespace TagLib {
        * Save the file.
        *
        * This returns true if the save was successful.
-       *
-       * \warning In the current implementation, it's dangerous to call save()
-       * repeatedly.  At worst it will corrupt the file.
        */
       virtual bool save();