Fix typo

In early development patches, "replication origins" were called "identifiers";
almost everything was renamed, but these references to the old terminology
went unnoticed.

Reported-by: Craig Ringer

src/backend/replication/logical/origin.c

@@ -1100,7 +1100,7 @@ replorigin_session_setup(RepOriginId node)
 		{
 			ereport(ERROR,
 					(errcode(ERRCODE_OBJECT_IN_USE),
-					 errmsg("replication identifier %d is already active for PID %d",
+					 errmsg("replication origin %d is already active for PID %d",
 							curstate->roident, curstate->acquired_by)));
 		}
 

src/include/catalog/pg_proc.dat

@@ -10555,7 +10555,7 @@
   prosrc => 'pg_replication_origin_xact_reset' },
 
 { oid => '6012',
-  descr => 'advance replication identifier to specific location',
+  descr => 'advance replication origin to specific location',
   proname => 'pg_replication_origin_advance', provolatile => 'v',
   proparallel => 'u', prorettype => 'void', proargtypes => 'text pg_lsn',
   prosrc => 'pg_replication_origin_advance' },