Payless Sales Drop, President Exits  NEW YORK (Reuters) - Footwear chain Payless ShoeSource Inc.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=PSS.N target=/stocks/quickinfo/fullquote"&gt;PSS.N&lt;/A&gt; on Thursday posted worse-than-expected sales at stores  open at least a year in August and said its president, Duane  Cantrell, will step down effective immediately, sending its  shares down 8 percent.