pgsql: Revert commit 606f350de9.

Revert commit 606f350de9.

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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REL9_5_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/dc06d0839a330d2a51ae10d1a168312b9daf7b0a

Modified Files
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src/backend/commands/tablecmds.c         | 67 +++++++++-----------------------
src/test/regress/expected/privileges.out | 21 ----------
src/test/regress/sql/privileges.sql      | 14 -------
3 files changed, 18 insertions(+), 84 deletions(-)