Consider adding citus_remove_rebalance_strategy()

[onurctirtir]

It'd be convenient to have citus_remove_rebalance_strategy() as opposite of citus_add_rebalance_strategy().

Then, we'd also want to expand the surface of pg_dist_rebalance_strategy_trigger_func() from BEFORE OR INSERT to BEFORE OR INSERT OR DELETE and perform necessary checks for DELETE as well.

[JelteF]

I agree a UDF would be nice here. But I don't think many checks would need to be performed for delete. The main thing I'd be worried about is ending up without a default rebalance strategy.