[subprocess2] Replace VOID with DEVNULL

subprocess.DEVNULL was introduced in Python3 to serve same purpose
as subprocess2.VOID, so rename VOID to DEVNULL in subprocess2.

Change-Id: I6dade3306ffc3bc2441ac6083f362b099c2427e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2587758
Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
diff --git a/scm.py b/scm.py
index 4e1bdde..42f566b 100644
--- a/scm.py
+++ b/scm.py
@@ -75,8 +75,8 @@
     try:
       subprocess2.check_call(
           ['git', 'rev-parse', '--show-cdup'],
-          stdout=subprocess2.VOID,
-          stderr=subprocess2.VOID,
+          stdout=subprocess2.DEVNULL,
+          stderr=subprocess2.DEVNULL,
           cwd=root)
       return 'git'
     except (OSError, subprocess2.CalledProcessError):