mb: Fully remove references to 'masters' in favor of 'builder_groups'.

All of WebRTC's mb_configs should have been swapped over to using
'builder_groups'.

Bug: chromium:1117773, webrtc:11680
Change-Id: I5509c242ded0a381b781eef14c2514247eaedf1b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/201721
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Cr-Commit-Position: refs/heads/master@{#32987}
diff --git a/tools_webrtc/mb/mb.py b/tools_webrtc/mb/mb.py
index 358a66e..9134095 100755
--- a/tools_webrtc/mb/mb.py
+++ b/tools_webrtc/mb/mb.py
@@ -81,8 +81,6 @@
       subp.add_argument('-b', '--builder',
                         help='builder name to look up config from')
       subp.add_argument('-m', '--builder-group',
-                        # TODO(crbug.com/1117773): Remove the 'master' args.
-                        '--master',
                         help='builder group name to look up config from')
       subp.add_argument('-c', '--config',
                         help='configuration to analyze')