This file was replaced in cc193e0d1d9c63e606316e9ab90fa8dc60014949 (part of MDL-52154). See specifically, the locallib.php change

 git show cc193e0d1d9c63e606316e9ab90fa8dc60014949 mod/lti/locallib.php

At that point, this wasn't being passed to tools during registration, nor used anywhere else and should probably have just been deleted, but wasn't.

We've moved this up to core_ltix as part of MDL-79109, which is where I noticed it wasn't used for anything.

Let's just remove it after that project is done. This would also involve deprecation of any strings it uses exclusively.