pgsql: Remove redundant pg_set_*_stats() variants.

Remove redundant pg_set_*_stats() variants.

After commit f3dae2ae58, the primary purpose of separating the
pg_set_*_stats() from the pg_restore_*_stats() variants was
eliminated.

Leave pg_restore_relation_stats() and pg_restore_attribute_stats(),
which satisfy both purposes, and remove pg_set_relation_stats() and
pg_set_attribute_stats().

Reviewed-by: Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
Discussion: https://postgr.es/m/1457469.1740419458@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a5cbdeb98af9a8d4f683fbffa69cd74be1f4a084

Modified Files
--------------
doc/src/sgml/func.sgml | 254 +++---
src/backend/catalog/system_functions.sql | 32 -
src/backend/statistics/attribute_stats.c | 98 +-
src/backend/statistics/relation_stats.c | 24 +-
src/backend/statistics/stat_utils.c | 30 +-
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 32 +-
src/include/statistics/stat_utils.h | 8 +-
src/test/regress/expected/stats_import.out | 1339 ++++++++--------------------
src/test/regress/sql/stats_import.sql | 1075 +++++++---------------
10 files changed, 872 insertions(+), 2022 deletions(-)