Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/boxingOptimization/foldRange.kt

@@ -0,0 +1,11 @@
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+fun box(): String {
+    val result = (1..5).fold(0) { x, y -> x + y }
+
+    assertEquals(15, result)
+
+    return "OK"
+}