pgsql: Remove some unnecessary includes of "access/xlog_internal.h"

Remove some unnecessary includes of "access/xlog_internal.h"

There were a few places where access/xlog_internal.h was apparently
included unnecessarily.  In some of those places, a more specific
header file (that somehow came in via access/xlog_internal.h) can be
used instead.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://www.postgresql.org/message-id/flat/a56a6eec-eb14-471b-9570-3cac23603964%40eisentraut.org

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/90834ceccd7298d4495c088fab85e6d87b9cb086

Modified Files
--------------
src/bin/pg_checksums/pg_checksums.c | 2 +-
src/bin/pg_rewind/timeline.c        | 1 -
src/include/access/generic_xlog.h   | 2 +-
3 files changed, 2 insertions(+), 3 deletions(-)