pgsql: Revert "psql \dX: list extended statistics objects"

Revert "psql \dX: list extended statistics objects"

Reverts 891a1d0bca, because the new  psql command \dX only worked for
users users who can read pg_statistic_ext_data catalog, and most regular
users lack that privilege (the catalog may contain sensitive user data).

Reported-by: Noriyoshi Shinoda
Discussion: https://postgr.es/m/c027a541-5856-75a5-0868-341301e1624b%40nttcom.co.jp_1

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1db0d173a2201119f297ea35edfb41579893dd8c

Modified Files
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doc/src/sgml/ref/psql-ref.sgml          |  22 -----
src/bin/psql/command.c                  |   3 -
src/bin/psql/describe.c                 | 150 --------------------------------
src/bin/psql/describe.h                 |   3 -
src/bin/psql/help.c                     |   1 -
src/bin/psql/tab-complete.c             |   4 +-
src/test/regress/expected/stats_ext.out |  94 --------------------
src/test/regress/sql/stats_ext.sql      |  31 -------
8 files changed, 1 insertion(+), 307 deletions(-)