The extra indirection neeeded to access its members via its enclosing
ResultRelInfo seems pointless. Move all the fields from
PartitionRoutingInfo to ResultRelInfo.

Author: Amit Langote
Reviewed-by: Alvaro Herrera
Discussion: https://www.postgresql.org/message-id/CA%2BHiwqFViT47Zbr_ASBejiK7iDG8%3DQ1swQ-tjM6caRPQ67pT%3Dw%40mail.gmail.com