Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/arrays/hashMap.kt

@@ -0,0 +1,11 @@
+import java.util.HashMap
+
+fun HashMap<String, Int?>.set(index: String, elem: Int?) {
+    this.put(index, elem)
+}
+
+fun box(): String {
+    val s = HashMap<String, Int?>()
+    s["239"] = 239
+    return if (s["239"] == 239) "OK" else "Fail"
+}