Fix comments for the dshash_parameters struct.
A recent commit added a copy_function member to the
dshash_parameters struct, but it missed updating a couple of
comments that refer to the function pointer members of this struct.
One of those comments also refers to a tranche_name member and non-
arg variants of the function pointer members, all of which were
either removed during development or removed shortly after dshash
table support was committed.
Oversights in commits
8c0d7bafad,
d7694fc148, and
42a1de3013.
Discussion: https://postgr.es/m/
20240227045213.GA2329190%40nathanxps13