Update obsolete comment.
Commit
b52b7dc25, which moved code creating PartitionBoundInfo in
RelationBuildPartitionDesc() in partcache.c (relocated to partdesc.c
afterwards) to partbounds.c, should have updated this, but didn't.
Author: Etsuro Fujita
Reviewed-by: Alvaro Herrera
Backpatch-through: 12
Discussion: https://postgr.es/m/CAPmGK16Uxr%3DPatiGyaRwiQVLB7Y-GqbkK3AxRLVYzU0Czv%3DsEw%40mail.gmail.com