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/statistics/dependencies.c

@@ -14,8 +14,6 @@
 #include "postgres.h"
 
 #include "access/htup_details.h"
-#include "access/sysattr.h"
-#include "catalog/pg_operator.h"
 #include "catalog/pg_statistic_ext.h"
 #include "catalog/pg_statistic_ext_data.h"
 #include "lib/stringinfo.h"
@@ -27,7 +25,6 @@
 #include "parser/parsetree.h"
 #include "statistics/extended_stats_internal.h"
 #include "statistics/statistics.h"
-#include "utils/bytea.h"
 #include "utils/fmgroids.h"
 #include "utils/fmgrprotos.h"
 #include "utils/lsyscache.h"
@@ -35,6 +32,7 @@
 #include "utils/selfuncs.h"
 #include "utils/syscache.h"
 #include "utils/typcache.h"
+#include "varatt.h"
 
 /* size of the struct header fields (magic, type, ndeps) */
 #define SizeOfHeader		(3 * sizeof(uint32))

src/backend/statistics/extended_stats.c

@@ -21,7 +21,6 @@
 #include "access/htup_details.h"
 #include "access/table.h"
 #include "catalog/indexing.h"
-#include "catalog/pg_collation.h"
 #include "catalog/pg_statistic_ext.h"
 #include "catalog/pg_statistic_ext_data.h"
 #include "executor/executor.h"
@@ -29,7 +28,6 @@
 #include "commands/progress.h"
 #include "miscadmin.h"
 #include "nodes/nodeFuncs.h"
-#include "optimizer/clauses.h"
 #include "optimizer/optimizer.h"
 #include "parser/parsetree.h"
 #include "pgstat.h"
@@ -47,7 +45,6 @@
 #include "utils/rel.h"
 #include "utils/selfuncs.h"
 #include "utils/syscache.h"
-#include "utils/typcache.h"
 
 /*
  * To avoid consuming too much memory during analysis and/or too much space

src/backend/statistics/mcv.c

@@ -17,19 +17,15 @@
 #include <math.h>
 
 #include "access/htup_details.h"
-#include "catalog/pg_collation.h"
 #include "catalog/pg_statistic_ext.h"
 #include "catalog/pg_statistic_ext_data.h"
 #include "fmgr.h"
 #include "funcapi.h"
 #include "nodes/nodeFuncs.h"
-#include "optimizer/clauses.h"
 #include "statistics/extended_stats_internal.h"
 #include "statistics/statistics.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
-#include "utils/bytea.h"
-#include "utils/fmgroids.h"
 #include "utils/fmgrprotos.h"
 #include "utils/lsyscache.h"
 #include "utils/selfuncs.h"

src/backend/statistics/mvdistinct.c

@@ -25,16 +25,15 @@
 
 #include <math.h>
 
-#include "access/htup_details.h"
 #include "catalog/pg_statistic_ext.h"
 #include "catalog/pg_statistic_ext_data.h"
 #include "lib/stringinfo.h"
 #include "statistics/extended_stats_internal.h"
 #include "statistics/statistics.h"
 #include "utils/fmgrprotos.h"
-#include "utils/lsyscache.h"
 #include "utils/syscache.h"
 #include "utils/typcache.h"
+#include "varatt.h"
 
 static double ndistinct_for_combination(double totalrows, StatsBuildData *data,
 										int k, int *combination);