Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/when/stringOptimization/duplicatingItems.kt

@@ -0,0 +1,21 @@
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+fun foo(x : String) : String {
+    when (x) {
+        "abc" -> return "abc"
+        "efg", "ghi", "abc" -> return "efg_ghi"
+        else -> return "other"
+    }
+}
+
+fun box() : String {
+    assertEquals("abc", foo("abc"))
+    assertEquals("efg_ghi", foo("efg"))
+    assertEquals("efg_ghi", foo("ghi"))
+
+    assertEquals("other", foo("xyz"))
+
+    return "OK"
+}