Revert MAINTAIN privilege and pg_maintain predefined role.

This reverts the following commits: 4dbdb82513, c2122aae63,
5b1a879943, 9e1e9d6560, ff9618e82a, 60684dd834, 4441fc704d,
and b5d6382496.  A role with the MAINTAIN privilege may be able to
use search_path tricks to escalate privileges to the table owner.
Unfortunately, it is too late in the v16 development cycle to apply
the proposed fix, i.e., restricting search_path when running
maintenance commands.

Bumps catversion.

Reviewed-by: Jeff Davis
Discussion: https://postgr.es/m/E1q7j7Y-000z1H-Hr%40gemulon.postgresql.org
Backpatch-through: 16

doc/src/sgml/ref/cluster.sgml

@@ -70,8 +70,9 @@ CLUSTER [VERBOSE]
    <command>CLUSTER</command> without a
    <replaceable class="parameter">table_name</replaceable> reclusters all the
    previously-clustered tables in the current database that the calling user
-   has privileges for.  This form of <command>CLUSTER</command> cannot be
-   executed inside a transaction block.
+   owns, or all such tables if called by a superuser.  This
+   form of <command>CLUSTER</command> cannot be executed inside a transaction
+   block.
   </para>
 
   <para>
@@ -132,11 +133,6 @@ CLUSTER [VERBOSE]
  <refsect1>
   <title>Notes</title>
 
-   <para>
-    To cluster a table, one must have the <literal>MAINTAIN</literal> privilege
-    on the table.
-   </para>
-
    <para>
     In cases where you are accessing single rows randomly
     within a table, the actual order of the data in the