Revert "Use GetCodeOwnersClient in presubmit_support"

This reverts commit 7a67bca65a00c8cb34cf4d73d30fc36c450d5b72.

Reason for revert: Probably broke chromium presubmit, see https://ci.chromium.org/ui/p/chromium/builders/try/chromium_presubmit/1152280/overview

Original change's description:
> Use GetCodeOwnersClient in presubmit_support
>
> This change also adds a target_ref flag to presubmit_support.py.
>
> Recipe-Nontrivial-Roll: build
> Change-Id: I6de6bb87fc1482b88d9fbebe5e4ad1dbd8ce9748
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2702792
> Commit-Queue: Gavin Mak <gavinmak@google.com>
> Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
> Reviewed-by: Josip Sokcevic <sokcevic@google.com>

Change-Id: I2cca469f14194f65306baab7928ddddd48033a3b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2718691
Auto-Submit: Stephen Martinis <martiniss@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
diff --git a/owners_client.py b/owners_client.py
index 915412e..14c1bf5 100644
--- a/owners_client.py
+++ b/owners_client.py
@@ -228,6 +228,6 @@
 
   Defaults to GerritClient, and falls back to DepotToolsClient if code-owners
   plugin is not available."""
-  if host and gerrit_util.IsCodeOwnersEnabled(host):
+  if gerrit_util.IsCodeOwnersEnabled(host):
     return GerritClient(host, project, branch)
   return DepotToolsClient(root, branch)