Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/reflection/properties/privateToThisAccessors.kt

@@ -0,0 +1,19 @@
+// WITH_REFLECT
+
+import kotlin.reflect.*
+import kotlin.reflect.jvm.*
+
+class K<in T : String> {
+    private var t: T
+        get() = "OK" as T
+        set(value) {}
+
+    fun run(): String {
+        val p = K::class.memberProperties.single() as KMutableProperty1<K<String>, String>
+        p.isAccessible = true
+        p.set(this as K<String>, "")
+        return p.get(this) as String
+    }
+}
+
+fun box() = K<String>().run()