Revert "Use pylint 2.7 for depot_tools"

This reverts commit 22bf605bb6.

Reason for revert: breaks gclient sync

Original change's description:
> Use pylint 2.7 for depot_tools
>
> This includes a few fixes for specific errors, and disables several new
> warnings introduced in this version, in order to allow for an incremental migration.
>
> Bug:1262286
> Change-Id: Ie97d686748c9c952e87718a65f401c5f6f80a5c9
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3400616
> Reviewed-by: Gavin Mak <gavinmak@google.com>
> Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>

Bug: 1262286
Change-Id: Ieb946073c7886c7bf056ce843a5a48e82becf7a5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3413672
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>

tests/git_find_releases_test.py

@@ -42,11 +42,9 @@ class TestGitFindReleases(unittest.TestCase):
       assert len(args) > 1
       if args[0] == 'name-rev' and args[1] == '--tags':
         return 'undefined'
-
-      if args[0] == 'name-rev' and args[1] == '--refs':
+      elif args[0] == 'name-rev' and args[1] == '--refs':
         return '1.0.0'
-
-      if args[0] == 'log':
+      elif args[0] == 'log':
         return ''
       assert False, "Unexpected arguments for git.run"