KtVisitor: delegate constructors to KtNamedDeclaration

In particular, enables back "Unused symbol" on constructors

compiler/frontend/src/org/jetbrains/kotlin/psi/KtVisitor.java

@@ -42,11 +42,11 @@ public class KtVisitor<R, D> extends PsiElementVisitor {
     }
 
     public R visitSecondaryConstructor(@NotNull KtSecondaryConstructor constructor, D data) {
-        return visitDeclaration(constructor, data);
+        return visitNamedDeclaration(constructor, data);
     }
 
     public R visitPrimaryConstructor(@NotNull KtPrimaryConstructor constructor, D data) {
-        return visitDeclaration(constructor, data);
+        return visitNamedDeclaration(constructor, data);
     }
 
     public R visitNamedFunction(@NotNull KtNamedFunction function, D data) {