Revert "Fix printing error on git-rebase failure"

This reverts commit 4511b131.

Reason for revert: Broke git_rebase_update.py under Python3, which does
not support calling decode() on string objects.

Original change's description:
> Fix printing error on git-rebase failure
> 
> R=​ehmaldonado@chromium.org
> 
> Bug: 1071280
> Change-Id: I8b1f00bb7c454297b10d5e047ae35c2686f69fb1
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2155154
> Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
> Commit-Queue: Josip Sokcevic <sokcevic@google.com>

TBR=ehmaldonado@chromium.org,infra-scoped@luci-project-accounts.iam.gserviceaccount.com,sokcevic@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1071280, 1073768
Change-Id: I58c1b24ba2aef255068c81be25475b2abbbf4fcb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2161111Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>

git_rebase_update.py

@@ -197,8 +197,8 @@ def rebase_branch(branch, parent, start_hash):
         else:
           print("Here's what git-rebase (squashed) had to say:")
           print()
-          print(squash_ret.stdout.decode('utf-8'))
-          print(squash_ret.stderr.decode('utf-8'))
+          print(squash_ret.stdout)
+          print(squash_ret.stderr)
           print(textwrap.dedent("""\
           Squashing failed. You probably have a real merge conflict.