Remove obsolete, confusing Harbormaster builds steps

Summary: Fixes T10458. These steps are obsolete and have not worked since the last updates to Drydock. They may eventually return in some form, but get rid of them for now since they're confusing.

Test Plan:

• Created a build plan with these steps.
• Removed these steps.
• Verified the build plan showed that the steps were invalid, and that I could delete them.
• Deleted them.
• Added new steps, no obsolete steps were available for selection.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10458

Differential Revision: https://secure.phabricator.com/D15352