Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/closures/enclosingThis.kt

@@ -0,0 +1,12 @@
+class Point(val x:Int, val y:Int) {
+    fun mul() :  (scalar:Int)->Point  {
+        return { (scalar:Int):Point -> Point(x * scalar, y * scalar) }
+    }
+}
+
+val m = Point(2, 3).mul() :  (scalar:Int)->Point
+
+fun box() : String {
+    val answer = m(5)
+    return if (answer.x == 10 && answer.y == 15) "OK" else "FAIL"
+}