Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/functions/defaultargs4.kt

@@ -0,0 +1,20 @@
+trait A {
+    fun bar2(arg: Int = 239) : Int
+
+    fun bar(arg: Int = 240) : Int = bar2(arg/2)
+}
+
+open abstract class B() : A, java.lang.Object() {
+    override fun bar2(arg: Int) : Int = arg
+}
+
+class C() : B() {
+}
+
+fun box() : String {
+    if(C().bar(10) != 5) return "fail"
+    if(C().bar() != 120) return "fail"
+    if(C().bar2() != 239) return "fail"
+    if(C().bar2(10) != 10) return "fail"
+    return "OK"
+}