Don't use parentheses for `echo` unnecessarily

Summary: As established in D10122.

Test Plan: I basically ran `arc lint --everything --apply-patches`.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10437