Remove magic "help" in global search

Summary: Fixes T7425. Overall, this is surprising and confusing after jump nav was merged with global search.

Test Plan: Searched for "help", got documents matching the word "help".

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: chasemp, epriestley

Maniphest Tasks: T7425

Differential Revision: https://secure.phabricator.com/D11936