Remove chrome/browser/sync from base::Callback PRESUBMIT allowlist

There are no remaining usages of base::Callback/base::Bind() in this
directory since crrev.com/c/2527142.

Change-Id: I8c18a0d777939937ba641fe17878f712ae9b1966
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2572337
Commit-Queue: Victor Vianna <victorvianna@google.com>
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Auto-Submit: Victor Vianna <victorvianna@google.com>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833437}

PRESUBMIT.py

@@ -364,7 +364,6 @@ _NOT_CONVERTED_TO_MODERN_BIND_AND_CALLBACK = '|'.join((
   '^chrome/browser/ssl/',
   '^chrome/browser/supervised_user/',
   '^chrome/browser/sync_file_system/',
-  '^chrome/browser/sync/',
   '^chrome/browser/thumbnail/cc/',
   '^chrome/browser/translate/',
   '^chrome/browser/ui/',