pgsql: Revert "Fix parallel-safety check of expressions and predicate f

Revert "Fix parallel-safety check of expressions and predicate for index builds"

This reverts commit eae7be600be7, following a discussion with Tom Lane,
due to concerns that this impacts the decisions made by the planner for
the number of workers spawned based on the inlining and const-folding of
index expressions and predicate for cases that would have worked until
this commit.

Discussion: https://postgr.es/m/162802.1709746091@sss.pgh.pa.us
Backpatch-through: 12

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/c46817ee512afa156561cce2dd6dc8440fe98d55

Modified Files
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src/backend/optimizer/plan/planner.c      | 12 +-----
src/backend/utils/cache/lsyscache.c       | 68 -------------------------------
src/include/utils/lsyscache.h             |  2 -
src/test/regress/expected/btree_index.out | 19 ---------
src/test/regress/sql/btree_index.sql      | 22 ----------
5 files changed, 2 insertions(+), 121 deletions(-)