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/postmaster/postmaster.c

@@ -91,18 +91,15 @@
 
 #include "access/xlog.h"
 #include "access/xlogrecovery.h"
-#include "catalog/pg_control.h"
 #include "common/file_perm.h"
 #include "common/file_utils.h"
 #include "common/ip.h"
 #include "common/pg_prng.h"
 #include "common/string.h"
 #include "lib/ilist.h"
-#include "libpq/auth.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
 #include "libpq/pqsignal.h"
-#include "nodes/queryjumble.h"
 #include "pg_getopt.h"
 #include "pgstat.h"
 #include "port/pg_bswap.h"
@@ -119,7 +116,6 @@
 #include "replication/walsender.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
-#include "storage/pg_shmem.h"
 #include "storage/pmsignal.h"
 #include "storage/proc.h"
 #include "tcop/tcopprot.h"
@@ -133,6 +129,8 @@
 #include "utils/varlena.h"
 
 #ifdef EXEC_BACKEND
+#include "nodes/queryjumble.h"
+#include "storage/pg_shmem.h"
 #include "storage/spin.h"
 #endif