Revert "depot_tools: Use vpython to execute fetch."

This reverts commit 028367fe.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> depot_tools: Use vpython to execute fetch.
> 
> Bug: 1002153
> Change-Id: I11286bebc23bedada239d6ddb8ebb86207a41485
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1815707
> Reviewed-by: Anthony Polito <apolito@google.com>
> Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
> Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>

TBR=tandrii@google.com,ehmaldonado@chromium.org,apolito@google.com

Change-Id: I0924e77a3862b8a75195db7fe719286e1cb3ac7e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1002153
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1824217Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

fetch

@@ -5,8 +5,4 @@
 
 base_dir=$(dirname "$0")
 
-# Ensure that "depot_tools" is somewhere in PATH so this tool can be used
-# standalone, but allow other PATH manipulations to take priority.
-PATH=$PATH:$base_dir
-
-PYTHONDONTWRITEBYTECODE=1 exec vpython "$base_dir/fetch.py" "$@"
+PYTHONDONTWRITEBYTECODE=1 exec python "$base_dir/fetch.py" "$@"

fetch.bat

@@ -12,4 +12,4 @@ call "%~dp0\update_depot_tools.bat"
 set PATH=%PATH%;%~dp0
 
 :: Defer control.
-vpython "%~dp0\fetch.py" %*
+python "%~dp0\fetch.py" %*

fetch.py

-#!/usr/bin/env vpython
+#!/usr/bin/env python
 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.