pgsql: Revert commit de0177788b.

Revert commit de0177788b.

This commit reverts the fix "Make inherited TRUNCATE perform access
permission checks on parent table only" only in the back branches.

It's not hard to imagine that there are some applications expecting
the old behavior and the fix breaks their security. To avoid this
compatibility problem, we decided to apply the fix only in HEAD and
revert it in all supported back branches.

Discussion: https://postgr.es/m/21015.1580400165@sss.pgh.pa.us

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0d9f307cf82a96bc7945c9eb86328abc14e55736

Modified Files
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src/backend/commands/tablecmds.c         | 32 +++++++-------------------------
src/test/regress/expected/privileges.out | 21 ---------------------
src/test/regress/sql/privileges.sql      | 14 --------------
3 files changed, 7 insertions(+), 60 deletions(-)