Whenever Netlify initializes a new build, it installs PHP, Ruby, Python and Go, which takes quite a while. And I use none of these things. Can I somehow make Netlify just not install them at all?
No, it’s not currently possible.
I understand you all have a lot of priorities to juggle, but nearly half my build time is spent installing EOL’d languages that I imagine very few Netlify customers actually use, even on the latest deploy image. It’s genuinely surprising there’s no exposed configuration to disable or skip them them.
Exactly! It also seems like a huge waste of CPU cycles and it’s not like the climate is in a great state 
Neither Go, Ruby nor Python is EOL’d and they’re all widely used.
Ruby is used by Jekyll,
Go is used by Hugo
and there are some static site builders with Python
PHP is probably the only one questionable, but even that’s not EOLd.