[v3] remove dup include in testcase

[Jonathan Wakely]

        * testsuite/20_util/shared_ptr/cons/55123.cc: Remove duplicate
        include.

Committed to trunk and 4.7

--- a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/55123.cc
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/55123.cc
@@ -22,8 +22,6 @@

 // libstdc++/55123

-#include <memory>
-
 void f() {
   std::unique_ptr<const int> y;
   std::shared_ptr<const int> x = std::move(y);