Remove issets on pay_later_receipt

Remove issets on pay_later_receipt

These issets were added to get tests passing with the later php version
which is now used on PR CI.

I think for these templates the value is always assigned so we can remove.

I am probably going to do a bunch of PRs removing issets to
hone in on which ones are actually still needed for the CI
so that I can put the work into the required ones