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/replication/logical/launcher.c

@@ -26,29 +26,22 @@
 #include "catalog/pg_subscription_rel.h"
 #include "funcapi.h"
 #include "lib/dshash.h"
-#include "libpq/pqsignal.h"
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "postmaster/bgworker.h"
-#include "postmaster/fork_process.h"
 #include "postmaster/interrupt.h"
-#include "postmaster/postmaster.h"
 #include "replication/logicallauncher.h"
-#include "replication/logicalworker.h"
 #include "replication/slot.h"
 #include "replication/walreceiver.h"
 #include "replication/worker_internal.h"
 #include "storage/ipc.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"
-#include "storage/procsignal.h"
 #include "tcop/tcopprot.h"
 #include "utils/builtins.h"
 #include "utils/memutils.h"
 #include "utils/pg_lsn.h"
-#include "utils/ps_status.h"
 #include "utils/snapmgr.h"
-#include "utils/timeout.h"
 
 /* max sleep time between cycles (3min) */
 #define DEFAULT_NAPTIME_PER_CYCLE 180000L