Undocument running multiple/dedicated pull daemons

Summary: In modern Phabricator, we should pretty much handle this automatically, and this advice is no longer very reasonable. See <https://github.com/phacility/phabricator/issues/660>

Test Plan: Read documentation.

Reviewers: chad, joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D9738