kt-1760 delegation to java iface:

- removed codegen's unnecessary lookup for a declaration
- skipped class' only supertype (if any) methods when delegating

compiler/testData/diagnostics/tests/DelegationToJavaIface.kt

@@ -0,0 +1,3 @@
+class TestIface(r : Runnable) : Runnable by r {}
+
+class TestObject(o : Object) : <!DELEGATION_NOT_TO_TRAIT!>Object<!> by o {}