Remove waits before fetching pages in batch activities

> We should eventually fix (not in this PR) this but there's no reason to wait before fetching the next page if we have executors that are free to pick up work.

https://github.com/temporalio/temporal/blob/main/service/worker/batcher/activities.go#L132-L150

https://github.com/temporalio/temporal/pull/8081/files#r2226888751