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/kt940.kt

@@ -0,0 +1,17 @@
+import java.util.*
+
+fun box() : String {
+    val w = object : Comparator<String?> {
+
+        override fun compare(o1 : String?, o2 : String?) : Int {
+            val l1 : Int = o1?.length ?: 0
+            val l2 = o2?.length ?: 0
+            return l1 - l2
+        }
+
+         override fun equals(obj: Any?): Boolean = obj === this
+    }
+
+    w.compare("aaa", "bbb")
+    return "OK"
+}