Replace nextstrain remote with aws commands

[j23414]

Description

From personal correspondence, use aws s3 to upload the metadata and sequence files.

nextstrain remote is not intended for general S3 operations (e.g. operations not on dataset JSON or narrative Markdown files).

Mostly this only influences build documentation, and may even be a non-issue as pathogen builds move away from fauna.

• [ ] https://github.com/nextstrain/fauna/blob/master/builds/DENGUE.md#push-to-s3
• [ ] https://github.com/nextstrain/fauna/blob/master/builds/MEASLES.md#push-to-s3
• [ ] https://github.com/nextstrain/fauna/blob/master/builds/ZIKA.md#push-to-s3