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/storage/file/buffile.c

@@ -49,8 +49,8 @@
 #include "executor/instrument.h"
 #include "miscadmin.h"
 #include "pgstat.h"
-#include "storage/buf_internals.h"
 #include "storage/buffile.h"
+#include "storage/bufmgr.h"
 #include "storage/fd.h"
 #include "utils/resowner.h"
 

src/backend/storage/file/fileset.c

@@ -23,14 +23,11 @@
 
 #include <limits.h>
 
-#include "catalog/pg_tablespace.h"
 #include "commands/tablespace.h"
 #include "common/file_utils.h"
 #include "common/hashfn.h"
 #include "miscadmin.h"
-#include "storage/ipc.h"
 #include "storage/fileset.h"
-#include "utils/builtins.h"
 
 static void FileSetPath(char *path, FileSet *fileset, Oid tablespace);
 static void FilePath(char *path, FileSet *fileset, const char *name);

src/backend/storage/file/sharedfileset.c

@@ -20,14 +20,8 @@
 
 #include <limits.h>
 
-#include "catalog/pg_tablespace.h"
-#include "commands/tablespace.h"
-#include "common/hashfn.h"
-#include "miscadmin.h"
 #include "storage/dsm.h"
-#include "storage/ipc.h"
 #include "storage/sharedfileset.h"
-#include "utils/builtins.h"
 
 static void SharedFileSetOnDetach(dsm_segment *segment, Datum datum);