Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/casts/asWithGeneric.kt

@@ -0,0 +1,23 @@
+// WITH_RUNTIME
+
+fun <T> test1() = null as T
+fun <T> test2(): T {
+   val a : Any? = null
+   return a as T
+}
+
+fun <T: Any> test3() = null as T
+
+fun box(): String {
+    if (test1<Int?>() != null) return "fail: test1"
+    if (test2<Int?>() != null) return "fail: test2"
+    var result3 = "fail"
+    try {
+        test3<Int>()
+    }
+    catch(e: TypeCastException) {
+        result3 = "OK"
+    }
+    if (result3 != "OK") return "fail: test3"
+    return "OK"
+}