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: I4b8f8fc521386419a3121bbb07edc8ac83170a94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3413679
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>
diff --git a/git_number.py b/git_number.py
index 1252833..f46b1ee 100755
--- a/git_number.py
+++ b/git_number.py
@@ -62,8 +62,8 @@
   """
   if sys.version_info.major == 3:
     return '/'.join('%02x' % b for b in hash_prefix)
-  else:
-    return '/'.join('%02x' % ord(b) for b in hash_prefix)
+
+  return '/'.join('%02x' % ord(b) for b in hash_prefix)
 
 
 @git.memoize_one(threadsafe=False)