There is no limit - predefined or configurable. Both tables will grow as long as you trigger events for data to be collected. The alf_activitiy_feed table may have data removed after a certain amount of time has passed (entries older than X days) while the alf_audit_entry table will only have data removed when entries are cleared via API (no automatic removal).
You could "disable" the cleaner by setting a CRON expression that effectively will never trigger the cleaner (activities.feed.cleaner.cronExpression). Or change the max allowed age of the feed (activities.feed.max.ageMins).