Description of proposed changes

Removes scripts, dependencies, docs, and rules for running pangolin as part of this workflow.

Related issue(s)

Related to nextstrain/docker-base#157

Testing

• CI tests pass

Release checklist

If this pull request introduces backward incompatible changes, complete the following steps for a new release of the workflow:

• Determine the version number for the new release by incrementing the most recent release (e.g., "v2" from "v1").
• Update docs/src/reference/change_log.md in this pull request to document these changes and the new version number.
• After merging, create a new GitHub release with the new version number as the tag and release title.