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/kt594.kt

@@ -0,0 +1,16 @@
+package array_test
+
+fun box() : String {
+    var array : IntArray? = IntArray(10)
+    array?.set(0, 3)
+    if(array?.get(0) != 3) return "fail"
+
+    var a = arrayOfNulls<Array<String?>>(5)
+    var b = arrayOfNulls<String>(1)
+    b.set(0, "239")
+    a?.set(0, b)
+
+    if(a?.get(0)?.get(0) != "239") return "fail"
+
+    return "OK"
+}