Remove unused local typedef

This fixes the following warning in gcc 4.8.2:
```
/home/ondrej/repos/csympy/src/teuchos/Teuchos_RCP.hpp: In function ‘Teuchos::RCP<T1> Teuchos::rcpWithInvertedObjOwnership(const Teuchos::RCP<T1>&, const Teuchos::RCP<T2>&)’:
/home/ondrej/repos/csympy/src/teuchos/Teuchos_RCP.hpp:648:44: warning: typedef ‘Pair_t’ locally defined but not used [-Wunused-local-typedefs]
   typedef std::pair<RCP<T>, RCP<ParentT> > Pair_t;
                                            ^
```