Revert "Remove the WITH_CSYMPY_RCP=no possibility"

This reverts commit 565b4449e28515127f310b973e0d814966009712.
Travis: test that it compiles with Teuchos::RCP

This is important to assure that we follow exactly the same API as Teuchos.
But do not run any tests, since they can't work (we now require our own RCP
implementation).