kv: remove follow-the-workload lease rebalancing?

Follow-the-workload has seen its time in the sun. Early in CRDB's history, it was part of the recommended topology patterns for multi-region clusters. However, it was never very good at its job. This is particularly true because follow-the-workload relies on schemas happening to have been organized in a way that groups rows with the same locality affinity together in the KV keyspace so that they end up on the same range. This requirement for the feature to be effective was never documented and so it's doubtful that users ever achieved much success using it to automatically detect and react to sustained locality affinity. At best then, it was useful to automatically react to diurnal load movement which was otherwise locality agnostic.

With lease preferences, a new collection of SQL-level MR abstractions to precisely control data locality, REGIONAL BY ROW auto-rehoming, and an ever-expanding focus on performance predictability, it's not clear that it still has a role in the system. It's also not clear that any customers still use the feature. And yet, there is a performance and maintenance cost to retaining the feature.

Is it time to delete it?

Epic: CRDB-54644

Jira issue: CRDB-23905