Remove cachalot

We found cachalot to cause a lot of issues in the K8s setup with multiple containers under load.

We are unsure what caused them, and to mitigate them, we disabled cachalot. This caused all issues to go away, and to our surprise all features, including loading complex timetables in Chronos, were still reasonably fast (with no perceptible difference).

Thus, I conclude that cachalot's query caching does not have a real benefit these days, and we should rather focus on making SQL queries fast. As cachalot introduces a lot more complexity than it boosts performance, we should drop it.