Remove unused typedef

Exposed by change of compilation flags in the nightlies

(cherry picked from commit 2fb90345)

Rich/RichTools/src/RichMirrorSegFinder.cpp

@@ -82,8 +82,6 @@ StatusCode Rich::MirrorSegFinder::loadMirrors( const Rich::DetectorType rich )
   m_secMirrors[rich][0].clear();
   m_secMirrors[rich][1].clear();
 
-  typedef std::vector<std::string> StringV;
-
   // load the primary mirrors
   const auto & sphMirs = deRich->paramVect<std::string>("SphericalMirrorDetElemLocations");
   for ( const auto & L : sphMirs )