There is no way to mass delete them and there is probably no way--short of
just skipping the whole downloaded transaction thing--to avoid getting them.
You could change FIs.
The basic premise of Money is that you WANT to take the bank's data as
gospel. Beyond that, their design and marketing assumption is that just about
the only reason you use Money is precisely so you can download this stuff.
The problem is that in all too many cases the bank's data is just useless
garbage by the time it gets into Money. Their systems either were never
designed to support this kind of interface or are intentionally downright
hostile to it.