Mashes error severity DEBUG1-DEBUG5 into DEBUG

src/backend/utils/error/elog.c

@@ -4652,23 +4652,12 @@ error_severity(int elevel)
 
 	switch (elevel)
 	{
-		/* GPDB_12_MERGE_FIXME: In PostgreSQL, DEBUG1-DEBUG5 are all mashed together into just
-		 * DEBUG here. Why are we doing it differently? Revert to upstream version?
-		 */
 		case DEBUG1:
-			prefix = gettext_noop("DEBUG1");
-			break;
 		case DEBUG2:
-			prefix = gettext_noop("DEBUG2");
-			break;
 		case DEBUG3:
-			prefix = gettext_noop("DEBUG3");
-			break;
 		case DEBUG4:
-			prefix = gettext_noop("DEBUG4");
-			break;
 		case DEBUG5:
-			prefix = gettext_noop("DEBUG5");
+			prefix = gettext_noop("DEBUG");
 			break;
 		case LOG:
 		case LOG_SERVER_ONLY: