Minor mop-up for List improvements.
Fix a few places that were using written-out versions of the
pg_list.h macros that commit
cc99baa43 just improved, making them
also use those macros so as to gain whatever performance improvement
is to be had.
Discussion: https://postgr.es/m/CAApHDvpo1zj9KhEpU2cCRZfSM3Q6XGdhzuAS2v79PH7WJBkYVA@mail.gmail.com