Define MeshPerElemTest regardless of ExodusII

Even if we have ExodusII *and* XDR disabled, we'll still need this base
class for XDA tests.

Author: roystgnr

tests/mesh/mesh_elem_test.h

@@ -3,8 +3,6 @@
 
 #include "../geom/elem_test.h"
 
-#ifdef LIBMESH_HAVE_EXODUS_API
-
 #include "libmesh/mesh_serializer.h"
 
 using namespace libMesh;
@@ -117,6 +115,4 @@ class MeshPerElemTest : public PerElemTest<elem_type>
   }
 };
 
-#endif // LIBMESH_HAVE_EXODUS_API
-
 #endif // MESH_ELEM_TEST_H