Fix const qualification in prune_freeze_setup()
The const qualification of the presult argument to prune_freeze_setup()
is later cast away, so it was not correct. Remove it and add a comment
explaining that presult should not be modified.
Author: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/
fb97d0ae-a0bc-411d-8a87-
f84e7e146488%40eisentraut.org