chore: Remove inlined yarn

[sidharthachatterjee]

I'm forgetting why exactly we did this but it appears unnecessary and it's certainly a better idea to use a locally available yarn so that

• we don't completely opt out of updates that include bug fixes (I'm currently hitting one for retext not being found which is fixed when I upgrade)
• we don't inline all of yarn in our repo 😅

@pieh Do you remember why we did this and if it is necessary anymore? Maybe it was CI? I feel like there ought to be a better solution here nonetheless.

[pieh]

It was part of #22400

Because docker image for some of things running in CI use like yarn 1.10 or so which fails hard :)

This also made sure that everyone using repo is using same yarn and yarn.lock doesn't change randomly depending on used yarn version.

If we are hitting bugs in yarn - let's upgrade this "checked in" version instead