Fix file references inside some SGML comments

In some cases, the comments mentioning their own file or another file
were not correct.

Author: Josh Soref <jsoref@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CACZqfqCyhE-voJUrUkc3GQuDakfJKx1ViiCdY7B8tQwyL6727g%40mail.gmail.com

doc/src/sgml/appendix-obsolete-default-roles.sgml

@@ -1,6 +1,6 @@
-<!-- doc/src/sgml/obsolete-default-roles.sgml -->
+<!-- doc/src/sgml/appendix-obsolete-default-roles.sgml -->
 <!--
-  See doc/src/sgml/obsolete.sgml for why this file exists. Do not change the id attribute.
+  See doc/src/sgml/appendix-obsolete.sgml for why this file exists. Do not change the id attribute.
 -->
 
 <sect1 id="default-roles" xreflabel="default-roles">

doc/src/sgml/appendix-obsolete-pgreceivexlog.sgml

@@ -1,6 +1,6 @@
-<!-- doc/src/sgml/obsolete-pgxlogdump.sgml -->
+<!-- doc/src/sgml/appendix-obsolete-pgreceivexlog.sgml -->
 <!--
-  See doc/src/sgml/obsolete.sgml for why this file exists. Do not change the id attribute.
+  See doc/src/sgml/appendix-obsolete.sgml for why this file exists. Do not change the id attribute.
 -->
 
 <sect1 id="app-pgreceivexlog" xreflabel="pg_receivexlog">

doc/src/sgml/appendix-obsolete-pgresetxlog.sgml

@@ -1,6 +1,6 @@
-<!-- doc/src/sgml/obsolete-pgresetxlog.sgml -->
+<!-- doc/src/sgml/appendix-obsolete-pgresetxlog.sgml -->
 <!--
-  See doc/src/sgml/obsolete.sgml for why this file exists. Do not change the id attribute.
+  See doc/src/sgml/appendix-obsolete.sgml for why this file exists. Do not change the id attribute.
 -->
 
 <sect1 id="app-pgresetxlog" xreflabel="pg_resetxlog">

doc/src/sgml/appendix-obsolete-pgxlogdump.sgml

@@ -1,6 +1,6 @@
-<!-- doc/src/sgml/obsolete-pgxlogdump.sgml -->
+<!-- doc/src/sgml/appendix-obsolete-pgxlogdump.sgml -->
 <!--
-  See doc/src/sgml/obsolete.sgml for why this file exists. Do not change the id attribute.
+  See doc/src/sgml/appendix-obsolete.sgml for why this file exists. Do not change the id attribute.
 -->
 
 <sect1 id="pgxlogdump" xreflabel="pg_xlogdump">

doc/src/sgml/appendix-obsolete-recovery-config.sgml

@@ -1,6 +1,6 @@
-<!-- doc/src/sgml/obsolete-recovery-config.sgml -->
+<!-- doc/src/sgml/appendix-obsolete-recovery-config.sgml -->
 <!--
-  See doc/src/sgml/obsolete.sgml for why this file exists. Do not change the id attribute.
+  See doc/src/sgml/appendix-obsolete.sgml for why this file exists. Do not change the id attribute.
 -->
 
 <sect1 id="recovery-config" xreflabel="recovery.conf">

doc/src/sgml/appendix-obsolete.sgml

@@ -1,4 +1,4 @@
-<!-- doc/src/sgml/obsolete.sgml -->
+<!-- doc/src/sgml/appendix-obsolete.sgml -->
 
 <appendix id="appendix-obsolete">
  <title>Obsolete or Renamed Features</title>

doc/src/sgml/backup-manifest.sgml

@@ -1,4 +1,4 @@
-<!-- doc/src/sgml/backupmanifest.sgml -->
+<!-- doc/src/sgml/backup-manifest.sgml -->
 
 <chapter id="backup-manifest-format">
  <title>Backup Manifest Format</title>