Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/objects/thisInConstructor.kt

@@ -0,0 +1,10 @@
+open class A(open val v: String) {
+}
+
+open class B(open val v: String) {
+  fun a(newv: String) = object: A("fail") {
+     override val v = this@B.v + newv
+  }
+}
+
+fun box() = B("O").a("K").v