Summary:
Using PhabricatorRobotsController overwrites robots.txt for blogs, URL shortener, and CDN domains. Using [PhabricatorRobotsPlatformController](https://we.phorge.it/book/dev/class/PhabricatorRobotsPlatformController/) should fix it.
Signed-off-by: Yongmin Hong <revi@omglol.email>
Test Plan: Reload personal-phorge.revicdn.net/robots.txt and it is not verbatim copy of issuetracker.revi.xyz/robots.txt
Reviewers: #acl_sudoers, #blessed_reviewers, revi
Reviewed By: #acl_sudoers, #blessed_reviewers, revi
Differential Revision: https://issuetracker.revi.xyz/D9
