Change pg_dump default for statistics export.

Set the default behavior of pg_dump and pg_dumpall to be
--no-statistics.

Leave the default for pg_restore and pg_upgrade to be
--with-statistics.

Discussion: https://postgr.es/m/CA+TgmoZ9=RnWcCOZiKYYjZs_AW1P4QXCw--h4dOLLHuf1Omung@mail.gmail.com
Reviewed-by: Greg Sabino Mullane <htamfids@gmail.com>
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>