VM: Remove unnecessary _Num class from runtime/lib.

runtime/lib/num.cc

Index: runtime/lib/num.cc
diff --git a/runtime/lib/num.cc b/runtime/lib/num.cc
deleted file mode 100644
index 8004c8c9d9e1937cd5aecf67cdb2d9122b906689..0000000000000000000000000000000000000000
--- a/runtime/lib/num.cc
+++ /dev/null
@@ -1,19 +0,0 @@
-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-#include "vm/bootstrap_natives.h"
-
-#include "vm/native_entry.h"
-#include "vm/object.h"
-
-namespace dart {
-
-DEFINE_NATIVE_ENTRY(Num_toString, 1) {
-  const Number& number = Number::CheckedHandle(arguments->NativeArgAt(0));
-  Heap::Space space = isolate->heap()->ShouldPretenure(kOneByteStringCid) ?
-      Heap::kPretenured : Heap::kNew;
-  return number.ToString(space);
-}
-
-}  // namespace dart