The listed numbers disagreed with the ones being used in the symbols;
but instead of just fixing the numbers in the comment, use the symbolic
name instead, which seems clearer.

This has been wrong all along, so apply back to 9.5 where BRIN was
introduced.

Reported-by: Tomas Vondra
Discussion: https://postgr.es/m/5ff514f2-8b1e-6366-b11c-8e2ed442562d@2ndquadrant.com