Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/arrays/nonNullArray.kt

@@ -0,0 +1,8 @@
+class A() {
+    class B(val i: Int) {
+    }
+
+    fun test() = Array<B> (10, { B(it) })
+}
+
+fun box() = if(A().test()[5].i == 5) "OK" else "fail"