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/tcop/cmdtag.c

@@ -13,7 +13,6 @@
  */
 #include "postgres.h"
 
-#include "miscadmin.h"
 #include "tcop/cmdtag.h"
 #include "utils/builtins.h"
 

src/backend/tcop/dest.c

@@ -39,7 +39,6 @@
 #include "executor/tstoreReceiver.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
-#include "utils/portal.h"
 
 
 /* ----------------

src/backend/tcop/fastpath.c

@@ -22,8 +22,8 @@
 #include "catalog/objectaccess.h"
 #include "catalog/pg_namespace.h"
 #include "catalog/pg_proc.h"
-#include "libpq/libpq.h"
 #include "libpq/pqformat.h"
+#include "libpq/protocol.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "port/pg_bswap.h"

src/backend/tcop/utility.c

@@ -16,13 +16,10 @@
  */
 #include "postgres.h"
 
-#include "access/htup_details.h"
 #include "access/reloptions.h"
 #include "access/twophase.h"
 #include "access/xact.h"
 #include "access/xlog.h"
-#include "catalog/catalog.h"
-#include "catalog/index.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_authid.h"
 #include "catalog/pg_inherits.h"
@@ -63,15 +60,11 @@
 #include "parser/parse_utilcmd.h"
 #include "postmaster/bgwriter.h"
 #include "rewrite/rewriteDefine.h"
-#include "rewrite/rewriteRemove.h"
 #include "storage/fd.h"
-#include "tcop/pquery.h"
 #include "tcop/utility.h"
 #include "utils/acl.h"
 #include "utils/guc.h"
 #include "utils/lsyscache.h"
-#include "utils/rel.h"
-#include "utils/syscache.h"
 
 /* Hook for plugins to get control in ProcessUtility() */
 ProcessUtility_hook_type ProcessUtility_hook = NULL;