44bf02fba2
We didn't really want it; it was only necessary because we wanted to use rtc::Optional<SdpAudioFormat>, and Optional used to require the contained type to be default constructable. But as of May 9th (https://codereview.webrtc.org/1896833004), it no longer does. Review-Url: https://codereview.webrtc.org/2066233002 Cr-Commit-Position: refs/heads/master@{#13211}