cli_snapshots: remove unused file run.py (#2950)

cli_snapshots/run.py

-#!/usr/bin/env python
-# Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-# This script is to execute build.rs during the GN build. See BUILD.gn.
-import subprocess
-import sys
-import os
-
-d = os.path.dirname(os.path.realpath(__file__))
-exe = sys.argv[1]
-env = os.environ.copy()
-env["CARGO_MANIFEST_DIR"] = d
-env["OUT_DIR"] = os.path.dirname(exe)
-# To match the behavior of cargo, we need to cd into this directory.
-os.chdir(d)
-sys.exit(subprocess.call([exe], env=env))