Fix ordering/categorization of some recently-added system views.

Somebody added pg_replication_origin, pg_replication_origin_status and
pg_replication_slots to catalogs.sgml without a whole lot of concern for
either alphabetical order or the difference between a table and a view.
Clean up the mess.

Back-patch to 9.5, not so much because this is critical as because if
I don't it will result in a cross-branch divergence in release-9.5.sgml,
which would be a maintenance hazard.

doc/src/sgml/high-availability.sgml

@@ -914,7 +914,7 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
     </para>
     <para>
      Existing replication slots and their state can be seen in the
-     <link linkend="catalog-pg-replication-slots"><structname>pg_replication_slots</structname></link>
+     <link linkend="view-pg-replication-slots"><structname>pg_replication_slots</structname></link>
      view.
     </para>
     <para>

doc/src/sgml/logicaldecoding.sgml

@@ -324,7 +324,7 @@ $ pg_recvlogical -d postgres --slot test --drop-slot
    <title>System Catalogs Related to Logical Decoding</title>
 
    <para>
-    The <link linkend="catalog-pg-replication-slots"><structname>pg_replication_slots</structname></link>
+    The <link linkend="view-pg-replication-slots"><structname>pg_replication_slots</structname></link>
     view and the
     <link linkend="monitoring-stats-views-table"><structname>pg_stat_replication</structname></link>
     view provide information about the current state of replication slots and

doc/src/sgml/release-9.5.sgml

@@ -2176,7 +2176,7 @@ Add GUC and storage parameter to set the maximum size of GIN pending list.
 -->
        <para>
         Report the processes holding replication slots in <link
-        linkend="catalog-pg-replication-slots"><structname>pg_replication_slots</></>
+        linkend="view-pg-replication-slots"><structname>pg_replication_slots</></>
         (Craig Ringer)
        </para>
 

doc/src/sgml/replication-origins.sgml

@@ -66,7 +66,7 @@
   <link linkend="pg-replication-origin-xact-setup"><function>pg_replication_origin_xact_setup()</function></link>.
   If that's done replication progress will persist in a crash safe
   manner. Replay progress for all replication origins can be seen in the
-  <link linkend="catalog-pg-replication-origin-status">
+  <link linkend="view-pg-replication-origin-status">
    <structname>pg_replication_origin_status</structname>
   </link> view. An individual origin's progress, e.g. when resuming
   replication, can be acquired using