Correct the handle URI for build steps

Summary: Fixes T9674. This was wrong to start with (URI is /edit/X/, not /X/edit/) but we have a new view page anyway.

Test Plan:

• Visited an exmaple URI in my browser.
• Followed a build step link from "Authorized By: ..." in Drydock.

Reviewers: joshuaspence, chad

Reviewed By: chad

Maniphest Tasks: T9674

Differential Revision: https://secure.phabricator.com/D14366