Summary:
- Move GC options into PHP.
- Remove the "run at" and "run for" options. The GC daemon doesn't actually do any table scans, is very gentle, and runs for like 3 seconds per day in any normal install. Just limit it to running once every 4 hours when it's caught up and call it a day.
Test Plan: Edited GC options.
Reviewers: btrahan, codeblock
Reviewed By: codeblock
CC: aran
Maniphest Tasks: T2255
Differential Revision: https://secure.phabricator.com/D4321
