Cleanup references to concurrent_links in gn binary.

Explicit pool are recommended and concurrent_links is deprecated.
Remove concurrent_links support as it should no longer be used.

BUG=612786

Review-Url: https://codereview.chromium.org/2211593002
Cr-Original-Commit-Position: refs/heads/master@{#409909}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 662a802270f017a00bc870f12866b8f581596d79
6 files changed
tree: 60a6c06b6e52d46d1235ef96f10b462a3c670763
  1. tools/