Remove dedicated "Jump Nav" navigation element
Summary: Fixes T5175. Not sure if I cleaned out everything, but this seemed like a reasonable first pass. Attempted to delete all code that belonged to Jump Nav feature only.
Test Plan: Open phabricator homepage, verify Jump Nav element is gone, verify the Search bar still autocompletes and jumps to shortcuts.
Reviewers: chad, epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: epriestley, Korvin
Maniphest Tasks: T5175
Differential Revision: https://secure.phabricator.com/D9301