Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/traits/multiple.kt

@@ -0,0 +1,21 @@
+trait AL {
+    fun get(index: Int) : Any? = null
+}
+
+trait ALE<T> : AL {
+    fun getOrNull(index: Int, value: T) : T {
+        val r = get(index) as? T
+        return r ?: value
+    }
+}
+
+open class SmartArrayList() : ALE<String> {
+}
+
+class SmartArrayList2() : SmartArrayList(), AL {
+}
+
+fun box() : String {
+  val c = SmartArrayList2()
+  return if("239" == c.getOrNull(0, "239")) "OK" else "fail"
+}