Move blackBoxFile() testData to box/ directory

Delete all test methods (and empty test classes), since they'll be
auto-generated

compiler/testData/codegen/box/classes/kt2566_2.kt

@@ -0,0 +1,17 @@
+open class A {
+    open val foo: String = "OK"
+}
+
+open class B : A() {
+    inner class E {
+        val foo: String = super<A>@B.foo
+    }
+}
+
+class C : B() {
+    inner class D {
+        val foo: String = super<B>@C.foo
+    }
+}
+
+fun box() = C().foo