[5.5] "Documentation" links are broken in the macro browser

Steps to reproduce

1. Bring up the page editor.
2. Bring up the Insert Macro dialog, choose Content by Label.
3. Click the "Documentation" link above the left-hand settings panel.

It takes you to the non-existent page http://<base-url>/pages/help.prefix

It should link to a URL like http://docs.atlassian.com/confluence/docs-54/Content+by+Label+Macro

This affects all help links in the create dialog and macro browser.