Remove obsolete, policy-violating "owners.query" API method

Summary: See https://hackerone.com/reports/1584409. This obsolete API method is technically policy-violating: Owners packages have had policies since D15275. See also T10360.

Test Plan: Viewed Conduit API console, no longer saw API method available.

Differential Revision: https://secure.phabricator.com/D21850