Revert "[infra] Use Python3 for our Presubmits"

This reverts commit 094bcdb9e5.

Reason for revert: Breaking Housekeeper-PerCommit-InfraTests_Linux. The bot will have to be updated as part of this change.

Original change's description:
> [infra] Use Python3 for our Presubmits
>
> https://source.chromium.org/chromium/chromium/tools/depot_tools/+/main:presubmit_support.py;l=319;drc=443d9135cc33f3156d5fe25ebec33f9adffbab65
>
> This also makes any errors from `make train -C infra/bots`
> look well formatted because check_output returns a bytestring
> in Python3 and when that is printed, the newlines et al are not
> rendered correctly. Thus we want the output of check_output
> to be encoded to UTF-8.
>
> Without setting the USE_PYTHON3 = True in PRESUBMIT.py,
> it appears that `git cl upload` would try to run our
> infra_tests.py in Python2 mode, which does not have
> the encoding argument for check_output.
>
> Apparently cipd_bin_packages/vpython3 does not have the
> "six" package installed (but cipd_bin_packages/vpython does)
> so I replaced the six.StringIO with io.StringIO, which
> is where that is located in Python3.
>
> Change-Id: Ic8f61bf943531583ba3d110a85260d69bdbf5eb2
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/537677
> Reviewed-by: Ravi Mistry <rmistry@google.com>
> Reviewed-by: Eric Boren <borenet@google.com>

Change-Id: I0becb25d155ce0b0281c25d83662f1b01aee8033
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/537777
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Ravi Mistry <rmistry@google.com>

PRESUBMIT.py

@@ -27,8 +27,6 @@ SERVICE_ACCOUNT_SUFFIX = [
         'skia-buildbots.google.com', 'skia-swarming-bots', 'skia-public',
         'skia-corp.google.com', 'chops-service-accounts']]
 
-USE_PYTHON3 = True
-
 
 def _CheckChangeHasEol(input_api, output_api, source_file_filter=None):
   """Checks that files end with at least one \n (LF)."""

infra/bots/infra_tests.py

@@ -21,7 +21,7 @@ SKIA_DIR = os.path.abspath(os.path.join(INFRA_BOTS_DIR, os.pardir, os.pardir))
 
 def test(cmd, cwd):
   try:
-    subprocess.check_output(cmd, cwd=cwd, stderr=subprocess.STDOUT, encoding='utf-8')
+    subprocess.check_output(cmd, cwd=cwd, stderr=subprocess.STDOUT)
   except subprocess.CalledProcessError as e:
     return e.output
 

tools/rewrite_includes.py

@@ -8,9 +8,10 @@
 
 import argparse
 import os
+import six
 import sys
 
-from io import StringIO
+from six import StringIO
 
 
 parser = argparse.ArgumentParser()