Shell Scraps Dual Ownership  LONDON/AMSTERDAM (Reuters) - Oil major Royal Dutch/Shell  Group &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=RD.AS target=/stocks/quickinfo/fullquote"&gt;RD.AS&lt;/A&gt;&lt;SHEL.L&gt; plans to move to a unified corporate  structure, ditching a century-old dual-ownership system blamed  for contributing to a reserves overbooking scandal.