(stable) Don't offer personal saved queries in global "Search Scope" settings dropdown
Summary: Fixes T13405. We currently offer non-global custom saved queries here, but this doesn't make sense as a global default setting.
Test Plan: Saved a global search query, edited global search settings, no longer saw the non-global query as an option.
Maniphest Tasks: T13405
Differential Revision: https://secure.phabricator.com/D20793