Merge boxWithStdlib testData into box, delete BoxWithStdlib test

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

@@ -0,0 +1,14 @@
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+inline fun <R> foo(x : R, block : (R) -> R) : R {
+    return block(x)
+}
+
+fun box() : String {
+    val result = foo(1) { x -> x + 1 }
+    assertEquals(2, result)
+
+    return "OK"
+}