doc: Remove reference to views for TRUNCATE privilege

The page about privilege rights mentioned that TRUNCATE could be applied
to views or even other relation types.  This is confusing as this
command can be used only on tables and on partitioned tables.

Oversight in afc4a78a.

Reported-by: Harisai Hari
Reviewed-by: Laurenz Albe
Discussion: https://postgr.es/m/161157636877.14625.15340884663716426087@wrigleys.postgresql.org
Backpatch-through: 12

doc/src/sgml/ddl.sgml

@@ -1740,7 +1740,7 @@ REVOKE ALL ON accounts FROM PUBLIC;
      <term><literal>TRUNCATE</literal></term>
      <listitem>
       <para>
-       Allows <command>TRUNCATE</command> on a table, view, etc.
+       Allows <command>TRUNCATE</command> on a table.
       </para>
      </listitem>
     </varlistentry>