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/kt1247.kt

@@ -0,0 +1,6 @@
+fun f(a : Int?, b : Int.(Int)->Int) = a?.b(1)
+
+fun box(): String {
+    val x = f(1) { this+it+2 }
+    return if (x == 4) "OK" else "fail"
+}