Remove SdpAudioFormat's default constructor

Remove SdpAudioFormat's default constructor

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.

Committed: https://crrev.com/44bf02fba2d0d6c2c1b08ea09e2a0cd2e8b93846
Cr-Commit-Position: refs/heads/master@{#13211}

[kwiberg-webrtc, 2016-06-15 11:48:18]

kwiberg@webrtc.org changed reviewers:
+ ossu@webrtc.org

[ossu, 2016-06-20 08:25:06]

lgtm

[kwiberg-webrtc, 2016-06-20 09:04:04]

The CQ bit was checked by kwiberg@webrtc.org

[commit-bot: I haz the power, 2016-06-20 09:04:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2066233002/1

[commit-bot: I haz the power, 2016-06-20 09:39:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-06-20 09:39:55]

Description was changed from

==========
Remove SdpAudioFormat's default constructor

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.
==========

to

==========
Remove SdpAudioFormat's default constructor

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.

Committed: https://crrev.com/44bf02fba2d0d6c2c1b08ea09e2a0cd2e8b93846
Cr-Commit-Position: refs/heads/master@{#13211}
==========

[commit-bot: I haz the power, 2016-06-20 09:39:56]

Patchset 1 (id:??) landed as
https://crrev.com/44bf02fba2d0d6c2c1b08ea09e2a0cd2e8b93846
Cr-Commit-Position: refs/heads/master@{#13211}