Remove unused #include's from backend .c files

as determined by include-what-you-use (IWYU)

While IWYU also suggests to *add* a bunch of #include's (which is its
main purpose), this patch does not do that.  In some cases, a more
specific #include replaces another less specific one.

Some manual adjustments of the automatic result:

- IWYU currently doesn't know about includes that provide global
  variable declarations (like -Wmissing-variable-declarations), so
  those includes are being kept manually.

- All includes for port(ability) headers are being kept for now, to
  play it safe.

- No changes of catalog/pg_foo.h to catalog/pg_foo_d.h, to keep the
  patch from exploding in size.

Note that this patch touches just *.c files, so nothing declared in
header files changes in hidden ways.

As a small example, in src/backend/access/transam/rmgr.c, some IWYU
pragma annotations are added to handle a special case there.

Discussion: https://www.postgresql.org/message-id/flat/af837490-6b2f-46df-ba05-37ea6a6653fc%40eisentraut.org

src/backend/backup/backup_manifest.c

@@ -15,8 +15,6 @@
 #include "access/timeline.h"
 #include "backup/backup_manifest.h"
 #include "backup/basebackup_sink.h"
-#include "libpq/libpq.h"
-#include "libpq/pqformat.h"
 #include "mb/pg_wchar.h"
 #include "utils/builtins.h"
 #include "utils/json.h"

src/backend/backup/basebackup.c

@@ -48,7 +48,6 @@
 #include "utils/ps_status.h"
 #include "utils/relcache.h"
 #include "utils/resowner.h"
-#include "utils/timestamp.h"
 
 /*
  * How much data do we want to send in one CopyData message? Note that

src/backend/backup/basebackup_incremental.c

@@ -20,15 +20,15 @@
 #include "postgres.h"
 
 #include "access/timeline.h"
-#include "access/xlog.h"
-#include "access/xlogrecovery.h"
 #include "backup/basebackup_incremental.h"
 #include "backup/walsummary.h"
 #include "common/blkreftable.h"
 #include "common/parse_manifest.h"
 #include "common/hashfn.h"
 #include "common/int.h"
+#include "datatype/timestamp.h"
 #include "postmaster/walsummarizer.h"
+#include "utils/timestamp.h"
 
 #define	BLOCKS_PER_READ			512
 

src/backend/backup/basebackup_progress.c

@@ -31,13 +31,9 @@
  */
 #include "postgres.h"
 
-#include "backup/basebackup.h"
 #include "backup/basebackup_sink.h"
 #include "commands/progress.h"
-#include "miscadmin.h"
 #include "pgstat.h"
-#include "storage/latch.h"
-#include "utils/timestamp.h"
 
 static void bbsink_progress_begin_backup(bbsink *sink);
 static void bbsink_progress_archive_contents(bbsink *sink, size_t len);

src/backend/backup/basebackup_server.c

@@ -11,13 +11,11 @@
 #include "postgres.h"
 
 #include "access/xact.h"
-#include "backup/basebackup.h"
 #include "backup/basebackup_sink.h"
 #include "catalog/pg_authid.h"
 #include "miscadmin.h"
 #include "storage/fd.h"
 #include "utils/acl.h"
-#include "utils/timestamp.h"
 #include "utils/wait_event.h"
 
 typedef struct bbsink_server