Remove outdated recommendation for manual VACUUM

We have had a working and tunable autovacuum
for at least a decade now, so remove the recommendation to
manually vacuum tables at least every night.
Autovacuum is now also triggered by INSERTs, so we can also
remove the recommendation to run VACUUM (ANALYZE) after lots
of INSERTs or DELETEs.

Instead, suggest using autovacuum by moving the respective
paragraph up to where the importance of VACUUM is emphasized.

Author: Laurenz Albe <laurenz.albe@cybertec.at>
Reviewed-By: Magnus Hagander, Peter Geoghegan
Discussion: https://postgr.es/m/6f5e3da98fec14640f389d7b84c3b413833697f4.camel@cybertec.at

doc/src/sgml/ref/vacuum.sgml

@@ -377,15 +377,11 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
    </para>
 
    <para>
-    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 <command>VACUUM
-    ANALYZE</command> command for the affected table. This will update the
-    system catalogs with
-    the results of all recent changes, and allow the
-    <productname>PostgreSQL</productname> query planner to make better
-    choices in planning queries.
+    We recommend that all databases be vacuumed regularly in
+    order to remove dead rows.  <productname>PostgreSQL</productname> includes
+    an <quote>autovacuum</quote> facility which can automate routine vacuum
+    maintenance.  For more information about automatic and manual vacuuming,
+    see <xref linkend="routine-vacuuming"/>.
    </para>
 
    <para>
@@ -412,12 +408,6 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
     details.
    </para>
 
-   <para>
-    <productname>PostgreSQL</productname> includes an <quote>autovacuum</quote>
-    facility which can automate routine vacuum maintenance.  For more
-    information about automatic and manual vacuuming, see
-    <xref linkend="routine-vacuuming"/>.
-   </para>
    <para>
     Each backend running <command>VACUUM</command> without the
     <literal>FULL</literal> option will report its progress in the