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/kt772.kt

@@ -0,0 +1,25 @@
+package demo2
+
+fun print(o : Any?) {}
+
+fun test(i : Int) {
+    var monthString : String? = "<empty>"
+        when (i) {
+        1 -> {
+            print(1)
+            print(2)
+            print(3)
+            print(4)
+            print(5)
+        }
+       else -> {
+            monthString = "Invalid month"
+        }
+    }
+    print(monthString)
+}
+
+fun box() : String {
+    for (i in 1..12) test(i)
+    return "OK"
+}