chore: replace snakemake message directive with comment

[corneliusroemer]

In our Nextstrain styleguide we discourage use of snakemake's message directive as it causes the rule name to be hidden, which is undesirable Instead, it's best to simply use triple comments

[corneliusroemer]

If you want to clean up further, I would suggest using snakefmt for the snakemake files and also potentially black as Python formatter 🙃