Fix "phd repository-launch-readonly"

Summary:

• Delete an unreachable block of code.
• Pass "--" to terminate overseer args.

Test Plan: Ran "phd repository-launch-readonly", didn't get argument errors out of the daemon.

Reviewers: jungejason

Reviewed By: jungejason

CC: aran

Differential Revision: https://secure.phabricator.com/D2456