QPID-5858: Remove unneeded line that generates a warning on Windows VS2010.

2>  MessagingSessionTests.cpp
2>..\..\..\cpp\src\tests\MessagingSessionTests.cpp(1438): warning C4930: 
  'std::string queue(void)': prototyped function not called (was a variable definition intended?)


git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1609726 13f79535-47bb-0310-9956-ffa450edef68