Where is this? I looked but didn't see it. Found the tool that checks for missing files, but nothing about orphaned files.
maybe I am mixing the tools?

I remember there was another tool for that (but It didn't checked for scripts)
on Stats, its here:

(it doesn't checks for script use either, so he will need to use a tool like
Notepad++ and use "search in files".
This will help to get rid of all unused content.
For example, there are 50 .bmp files spread in many folders (result of Rotsprite). And those files aren't being used for anything.
Use Notepadd++ "Search in files" (ctrl+shift+F) and put .txt on filters. This will help you to see if any entity is using those files.
or leave the filter alone so you can find all the usage in any type of file.
converting some animated gifs to webm
In some cases, it will work, in some will give you a bigger size file. It's a case by case subject (same for .gif and .png)
Some more tips about sound/music:
- you don't need stereo sound effects in most cases. Unless your sound file has some stereo panning effect, this will just make the file bigger
- I use my sound files in 22khz 16bit. You can increase it to 441khz if you want to. 8bit gives a smaller file size, but adds a lot of noise. Some old ports doesn't like 16bit sound files (wii, If I can remember right), but I doubt this game would run on it anyway
- You have to convert all the .ogg files to .wav and use OGGENC to convert it back to .ogg. No other tool can compress that much as that tool.
The fact that I can't use remix.ogg instead of remix.bor (we talk about it on the chat) is a known problem, so as for that file, I can't do anything. But it's not one of the biggest either.
Strange, because this were already fixed many years ago. I remember I had this issue back in 4420 I think, but this doesn't happens anymore in later builds as 6314 and 6330. Your build looks to be newer (7123).
edit: according to Stats, there are more than 5000 files not in use
But the tool doesn't checks for script usage, so proceed with caution