Revert "[test_env.py] Reland: Warm up vpython virtualenv cache on swarming task shards"

This reverts commit 21813050.

Reason for revert: Broke (at least) webrtc's deps roller and Mac bisectors

Original change's description:
> [test_env.py] Reland: Warm up vpython virtualenv cache on swarming task shards
> 
> This will prevent tests sensitive to cold vpython startup time from
> timing out.
> 
> Relands https://chromium-review.googlesource.com/c/chromium/src/+/917802 . We
> expect this to work because test shards now include a hermetic copy of
> cpython as well as vpython (which was the failure observed in
> crbug.com/812693).
> 
> R=​dpranke@chromium.org, kbr@chromium.org, tandrii@chromium.org
> 
> Bug: 804174,812693
> Change-Id: Ic38845f8af366d9af211bef64df135176ab9ee1d
> Reviewed-on: https://chromium-review.googlesource.com/933107
> Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
> Reviewed-by: Dirk Pranke <dpranke@chromium.org>
> Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#538652}

TBR=iannucci@chromium.org,dpranke@chromium.org,kbr@chromium.org,tandrii@chromium.org

Change-Id: Ia8f6a122db20332c67b2376a176b18c68ae9efd1
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 804174, 812693
Reviewed-on: https://chromium-review.googlesource.com/935028Reviewed-by: Charlie Andrews <charliea@chromium.org>
Commit-Queue: Charlie Andrews <charliea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538843}

testing/test_env.py

@@ -240,14 +240,6 @@ def run_executable(cmd, env, stdoutfile=None):
   cmd[0] = cmd[0].replace('/', os.path.sep)
   cmd = fix_python_path(cmd)
 
-  # Warm vpython virtualenv cache. Some tests are sensitive to vpython startup
-  # time when it has a cold cache (crbug.com/804174).
-  vpython = 'vpython.bat' if sys.platform == 'win32' else 'vpython'
-  subprocess.check_call([
-    vpython, '-vpython-spec', os.path.join(ROOT_DIR, '.vpython'),
-    '-vpython-tool', 'install',
-  ])
-
   print('Additional test environment:\n%s\n'
         'Command: %s\n' % (
         '\n'.join('    %s=%s' %