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/delegation2.kt

@@ -0,0 +1,24 @@
+trait Trait1 {
+    fun foo() : String
+}
+
+trait Trait2  {
+    fun bar() : String
+}
+
+class T1 : Trait1{
+    override fun foo() = "aaa"
+}
+
+class T2 : Trait2{
+    override fun bar()  = "bbb"
+}
+
+class C(a:Trait1, b:Trait2) : Trait1 by a, Trait2 by b
+
+fun box() : String {
+    val c = C(T1(),T2())
+    if(c.foo() != "aaa") return "fail"
+    if(c.bar() != "bbb") return "fail"
+    return "OK"
+}