/etc/polkit-1/localauthority.conf.d/51-ubuntu-admin.conf is in policykit-1 0.105-14.1ubuntu0.4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | [Configuration]
AdminIdentities=unix-group:sudo;unix-group:admin
|