Remove *pgaudit* references also.

Fixes the docs build.

doc/src/sgml/contrib.sgml

@@ -124,7 +124,6 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
  &ltree;
  &pageinspect;
  &passwordcheck;
- &pgaudit;
  &pgbuffercache;
  &pgcrypto;
  &pgfreespacemap;

doc/src/sgml/filelist.sgml

@@ -127,7 +127,6 @@
 <!ENTITY oid2name        SYSTEM "oid2name.sgml">
 <!ENTITY pageinspect     SYSTEM "pageinspect.sgml">
 <!ENTITY passwordcheck   SYSTEM "passwordcheck.sgml">
-<!ENTITY pgaudit         SYSTEM "pgaudit.sgml">
 <!ENTITY pgbuffercache   SYSTEM "pgbuffercache.sgml">
 <!ENTITY pgcrypto        SYSTEM "pgcrypto.sgml">
 <!ENTITY pgfreespacemap  SYSTEM "pgfreespacemap.sgml">