Stop reading input_api.tbr in PRESUBMIT.py

TBR is no longer supported, and depot_tools removed the --tbrs option
from git cl upload in https://chromium-review.googlesource.com/4185277.

Bug: chromium:40767138
Change-Id: If27e2f94ef5fd6e20eb9b4d5a5e0b7d9536a0b50
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/508840
Reviewed-by: Jeremy Leconte <jleconte@google.com>
Commit-Queue: Jeremy Leconte <jleconte@google.com>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48884}

PRESUBMIT.py

diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index a9d01cb..e53a31f 100755
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -1473,12 +1473,6 @@
         return []
 
     if input_api.is_committing:
-        if input_api.tbr:
-            return [
-                output_api.PresubmitNotifyResult(
-                    '--tbr was specified, skipping OWNERS check for DEPS '
-                    'additions')
-            ]
         if input_api.dry_run:
             return [
                 output_api.PresubmitNotifyResult(