doc: Remove inappropriate <acronym> tags

doc/src/sgml/brin.sgml

@@ -753,7 +753,7 @@ LOG:  request for BRIN range summarization for index "brin_wi_idx" page 128 was
    </variablelist>
 
    <para>
-    <acronym>minmax-multi</acronym> operator classes accept these parameters:
+    minmax-multi operator classes accept these parameters:
    </para>
 
    <variablelist>

doc/src/sgml/datatype.sgml

@@ -4925,7 +4925,7 @@ WHERE ...
   </sect1>
 
   <sect1 id="datatype-pg-lsn">
-   <title><acronym>pg_lsn Type</acronym></title>
+   <title><type>pg_lsn</type> Type</title>
 
    <indexterm zone="datatype-pg-lsn">
     <primary>pg_lsn</primary>

doc/src/sgml/release-14.sgml

@@ -1561,7 +1561,7 @@ Author: Peter Eisentraut <peter@eisentraut.org>
     </sect4>
 
     <sect4>
-     <title><acronym>Authentication</acronym></title>
+     <title>Authentication</title>
 
      <itemizedlist>