Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/reified/safecast.kt

@@ -0,0 +1,19 @@
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+inline fun<reified T> safecast(x: Any?): T? {
+    return x as? T
+}
+
+fun box(): String {
+    val x = safecast<String>("abc")
+    assertEquals("abc", x)
+    val y = safecast<Int>(1)
+    assertEquals(1, y)
+
+    val z = safecast<Int>("abc")
+    assertEquals(null, z)
+
+    return "OK"
+}