/usr/share/lightdm/lightdm.conf.d/50-greeter-wrapper.conf is in lightdm 1.26.0-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | [Seat:*]
greeter-wrapper=/usr/lib/lightdm/lightdm-greeter-session
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