SceneTools: remove unused test case declaration.

It's handled as an instance of indexFieldRvalue() already.

src/Magnum/SceneTools/Test/MapTest.cpp

@@ -54,7 +54,6 @@ struct MapTest: TestSuite::Tester {
 
     void indexFieldRvalue();
     void indexFieldRvalueSigned();
-    void indexFieldRvalueNamed();
     void indexFieldRvalueNotOwned();
     void indexFieldRvalueNotFullType();
 };