pgsql: Clean up some code and comments in partbounds.c.

Clean up some code and comments in partbounds.c.

Do some minor cleanup for commit c8434d64c: 1) remove a useless
assignment (in normal builds) and 2) improve comments a little.

Back-patch to v13 where the aforementioned commit went in.

Author: Etsuro Fujita
Reviewed-by: Alvaro Herrera
Discussion: https://postgr.es/m/CAPmGK16yCd2R4=bQ4g8N2dT9TtA5ZU+qNmJ3LPc_nypbNy4_2A@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/3857f98f143166f96c6f6359810ab4241ab4590f

Modified Files
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src/backend/partitioning/partbounds.c | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)