[tools] Switch script wrapper to Py3

Bug: chromium:1292013
Change-Id: I5d73c8a500d66143e569d4605133948a71c82c8b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3568468
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Commit-Queue: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79749}

tools/run.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright 2014 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
@@ -6,8 +6,6 @@
 """This program wraps an arbitrary command since gn currently can only execute
 scripts."""
 
-from __future__ import print_function
-
 import subprocess
 import sys