Remove recommendation for nightly VACUUM

A customer recently pointed me to
https://www.postgresql.org/docs/current/sql-vacuum.html
and asked if I agree with the statement there that a nightly
scheduled VACUUM were a good idea:

"We recommend that active production databases be vacuumed frequently
 (at least nightly), in order to remove dead rows. After adding or
 deleting a large number of rows, it might be a good idea to issue a
 VACUUM ANALYZE command for the affected table. This will update the
 system catalogs with the results of all recent changes, and allow the
 PostgreSQL query planner to make better choices in planning queries."

Looking at the Git history, most of that paragraph is from a time
when autovacuum did not yet exist or was much less reliable than it
is now.  So I suggest removing all that and pointing to autovacuum
instead, as done in the attached patch.

Yours,
Laurenz Albe