pgsql: Remove some more useless assignments.

Remove some more useless assignments.

Found with clang's scan-build tool. It also whines about a lot of
other dead stores that we should *not* change IMO, either as a matter
of style or future-proofing. But these places seem like clear
oversights.

Discussion: https://postgr.es/m/CAEudQAo1+AcGppxDSg8k+zF4+Kv+eJyqzEDdbpDg58-=MQcerQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/38a2d703298c9a891dc9c24c0c087f417f555c70

Modified Files
--------------
src/backend/access/brin/brin_tuple.c | 1 -
src/backend/access/gin/ginbtree.c | 1 -
src/backend/catalog/pg_depend.c | 6 +++---
src/backend/optimizer/plan/planner.c | 2 +-
src/backend/parser/parse_utilcmd.c | 1 -
src/backend/partitioning/partbounds.c | 4 ----
src/backend/statistics/extended_stats.c | 2 +-
src/backend/tsearch/spell.c | 4 ++--
8 files changed, 7 insertions(+), 14 deletions(-)