Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/objects/kt2663.kt

@@ -0,0 +1,10 @@
+fun box() : String {
+    var a = 1
+
+    object {
+        {
+            a = 2
+        }
+    }
+    return if (a == 2) "OK" else "fail"
+}