Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/controlStructures/kt769.kt

@@ -0,0 +1,11 @@
+package w_range
+
+fun box() : String {
+    var i = 0
+    when (i) {
+        1 -> i--
+        else -> { i = 2 }
+    }
+    System.out?.println(i)
+    return "OK"
+}