Hey there! This is a while after the fact, I know, but I've spent a couple hours today trying to figure this out, and yours was one of the few comments I found discussing removing specifically the survival mode HUD.
I have managed to figure out how to do that, and on the off chance you or someone else might find this information useful, I'll share it here.
Firstly, download and install this mod. Then, download and use OpenCAGE (The Open Source Alien Isolation Modding tool; there are other things with the same name that come up first if you google search just the name).
Use the "Game Asset Editor" -> "UI Import/Export" (to directly access UI.PAK without having to extract and recompile it) -> drill down into the file tree and delete CHALLENGELEADERBOARDCOMPONENT.GFX and CHALLENGEMAPOVERLAY.GFX files.
The game loads fine, loads the challenge maps just fine too, and in conjunction with all the rest of the UI being removed by the mod's initial tweaks, it completely removes all hud from the challenge mode maps! One minor downside is that there's now no prompts for what you need to do in the level, and UI once you complete the map, but that's basically no issue considering anyone who wants this change likely wants it to record footage and that's it; completing the level is unneccesary.
Hopefully at least one other person finds this helpful!
TheNoblestRoman
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