This reverts commit 10dbd7ba.

Reason for revert: removal broke builders

Original change's description:
> Remove old DepotToolsOwners implementation
>
> code-owners should have been enabled for most hosts that depot_tools
> supports by now. Remove our own implementation and rely on code-owners.
>
> Change-Id: Iaf0d3db65b2e5063b67d42b92188c4ec51d2cd9a
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3783475
> Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>
> Reviewed-by: Joanna Wang <jojwang@chromium.org>
> Commit-Queue: Gavin Mak <gavinmak@google.com>

Change-Id: I781648f470e8f2c9d408ae7112cfc41060f5385d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3818251
Auto-Submit: Gavin Mak <gavinmak@google.com>
Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>