Revert "Spawn via vpython when old module detected."

This reverts commit 28dfa45d60.

Reason for revert: No longer needed: https://crbug.com/1326517#c18

Original change's description:
> Spawn via vpython when old module detected.
>
> Not sure of a better way to detect this case as it seems to be running
> with the same python version as our vpython but modules are old.
>
> Bug: angleproject:7326
> Change-Id: I1750f65afdfdfc289af71bc7f426d5ba50dfd4a4
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3642804
> Commit-Queue: Roman Lavrov <romanl@google.com>
> Reviewed-by: Jamie Madill <jmadill@chromium.org>

Bug: angleproject:7326
Bug: chromium:1326517
Change-Id: I1940dafa54859b8b1c9f1c4f702381c4346c7e5b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3708994
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Roman Lavrov <romanl@google.com>

scripts/process_angle_perf_results.py

@@ -10,21 +10,14 @@
 
 from __future__ import print_function
 
-import os
-import six
-import sys
-# Swarming runs merge scripts with its python and some really old modules.
-if __name__ == '__main__' and 'ensure_binary' not in dir(six):
-    print('spawning via vpython due to an old six version (%s)' % six.__version__)
-    import subprocess
-    sys.exit(subprocess.call(['vpython', os.path.realpath(__file__)] + sys.argv[1:]))
-
 import argparse
 import collections
 import json
 import logging
 import multiprocessing
+import os
 import shutil
+import sys
 import tempfile
 import time
 import uuid