Revert "Skip WAL for new relfilenodes, under wal_level=minimal."

This reverts commit cb2fd7eac2.  Per
numerous buildfarm members, it was incompatible with parallel query, and
a test case assumed LP64.  Back-patch to 9.5 (all supported versions).

Discussion: https://postgr.es/m/20200321224920.GB1763544@rfd.leadboat.com

src/backend/utils/misc/guc.c

@@ -36,7 +36,6 @@
 #include "access/xlog_internal.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_authid.h"
-#include "catalog/storage.h"
 #include "commands/async.h"
 #include "commands/prepare.h"
 #include "commands/trigger.h"
@@ -2751,17 +2750,6 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
-	{
-		{"wal_skip_threshold", PGC_USERSET, WAL_SETTINGS,
-			gettext_noop("Size of new file to fsync instead of writing WAL."),
-			NULL,
-			GUC_UNIT_KB
-		},
-		&wal_skip_threshold,
-		2048, 0, MAX_KILOBYTES,
-		NULL, NULL, NULL
-	},
-
 	{
 		{"max_wal_senders", PGC_POSTMASTER, REPLICATION_SENDING,
 			gettext_noop("Sets the maximum number of simultaneously running WAL sender processes."),

src/backend/utils/misc/postgresql.conf.sample

@@ -215,7 +215,6 @@
 					# (change requires restart)
 #wal_writer_delay = 200ms		# 1-10000 milliseconds
 #wal_writer_flush_after = 1MB		# measured in pages, 0 disables
-#wal_skip_threshold = 2MB
 
 #commit_delay = 0			# range 0-100000, in microseconds
 #commit_siblings = 5			# range 1-1000