This was removed in #614 and accidentally re-introduced later in #603, which was merged afterwards.

Hmm, shouldn't the .gitignore entry have prevented it from being reintroduced?

https://github.com/WordPress/gutenberg/blob/2e68306/.gitignore#L3

Or is this not an expected behavior when merging a branch that is older than the gitignore changes?

I'm not entirely sure how that all works, but apparently simply having the .gitignore entry isn't always enough. (I guess I can think of a few ways to commit ignored files to a repository if you try hard enough, and now we know one more.)

Also I could've prevented this anyway by looking more closely at the changes in #603 before I merged it.

I should have noticed myself since I did the last rebase. I will try and pay more close attention in the future before asking for a merge.