Remove more-itertools dependency

[Florents-Tselai]

We use only one function which we should probably copy paste.

[edsu]

There's no harm in bringing it in for one function in my opinion.

[Florents-Tselai]

I believe we've too many dependencies for something relatively straightforward, and sooner or later, people will start being blocked by version paths that pip won't be able to resolve.

In an ideal world, the whole thing could be done with standard Python lib (since sqlite3 is standard Python)

[edsu]

In practice I don't think this is a big problem, unless we get stuck on some old versions of things. But there is certainly no harm in simplifying where you can!