removed old sourmash bam2fasta code

[phoenixAja]

Many thanks to contributing to nf-core/kmermaid!

Please fill in the appropriate checklist below (delete whatever is not relevant). These are the most common things requested on pull requests (PRs).

PR checklist

• [ ] PR is to dev rather than master
• [ ] This comment contains a description of changes (with reason)
• [ ] If you've fixed a bug or added code that should be tested, add tests!
• [ ] If necessary, also make a PR on the nf-core/kmermaid branch on the nf-core/test-datasets repo
• [ ] Ensure the test suite passes (nextflow run . -profile test,docker).
• [ ] Make sure your code lints (nf-core lint .).
• [ ] Documentation in docs is updated
• [ ] CHANGELOG.md is updated
• [ ] README.md is updated

Learn more about contributing: https://github.com/nf-core/kmermaid/tree/master/.github/CONTRIBUTING.md

[olgabot]

Thanks! Can you add a note in the changelog?