Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/reflection/mapping/syntheticFields.kt

@@ -0,0 +1,16 @@
+// WITH_REFLECT
+
+import kotlin.reflect.jvm.kotlin
+
+enum class A {
+    // There's a synthetic field "$VALUES" here
+}
+
+fun box(): String {
+    for (field in A::class.java.getDeclaredFields()) {
+        val prop = field.kotlin
+        if (prop != null) return "Fail, property found: $prop"
+    }
+
+    return "OK"
+}