Kibana version: 7.14

Describe the bug: When search sessions are disabled via xpack.data_enhanced.search.sessions.enabled: false, async searches are still created and have an expiration date a week in the future. This can lead to a lot of accumulated async search documents.

Steps to reproduce:

1. Set xpack.data_enhanced.search.sessions.enabled: false in kibana.yml
2. Go to Discover and do a few searches
3. Check async search documents via

GET .async-search/_search
{
  "_source": ["expiration_time"]
}

4. Expiration date is a week in the future

Expected behavior:
Expiration date should be very close to the current date and time or no async search documents should stick around