[m-dev.] stop generating .dep files using module_dep_file_v1 format

[Peter Wang]

On Sat, 31 Jul 2021 03:40:28 +1000 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> While working on the attached diff, I saw that we have not yet
> fully switched to module_dep_file_v2: we use v1 or v2 depending
> on whether a list is empty or not. Since using v1 gains us nothing
> other than not having to write out, and then read in, a single empty list,
> I propose that from now on, we should always write out .dep files
> using v2, because it will make the backward compatibility arrangements
> of any future v3 so much easier. Any objections?

No, that's fine.

Peter