Fix small paste-o in rice_distribution.

[Ed Smith-Rowland]

I initialized an adapted urng that was not needed or used in the 
rice_distribution extension.

2012-09-16  Edward Smith-Rowland  <3dw...@verizon.net>
        * include/ext/random.tcc (__gnu_cxx::rice_distribution<>
        ::__generate_impl): Remove bogus _Adaptor usage.

Index: include/ext/random.tcc
===================================================================
--- include/ext/random.tcc      (revision 191367)
+++ include/ext/random.tcc      (working copy)
@@ -762,9 +762,6 @@
       {
        __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator>)
 
-       std::__detail::_Adaptor<_UniformRandomNumberGenerator, result_type>
-         __aurng(__urng);
-
        while (__f != __t)
          {
            typename std::normal_distribution<result_type>::param_type