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/delegation4.kt

@@ -0,0 +1,28 @@
+open trait First {
+  public open fun foo() : Int
+}
+
+open trait Second : First {
+  public open fun bar() : Int
+}
+
+class Impl : Second {
+  public override fun foo() = 1
+  public override fun bar() = 2
+}
+
+class Test(s : Second) : Second by s {}
+
+fun box() : String {
+    var t = Test(Impl())
+    if (t.foo() != 1)
+        return "Fail #1"
+    if (t.bar() != 2)
+        return "Fail #2"
+    if (t !is First)
+        return "Fail #3"
+    if (t !is Second)
+        return "Fail #4"
+
+    return "OK"
+}