Revert of Adding the ability to create an RtpSender without a track.

Revert of Adding the ability to create an RtpSender without a track. (patchset #8 id:140001 of https://codereview.webrtc.org/1413713003/ )

Reason for revert:
Causing a compiler warning, and causing WebRtcBrowserTest.CallAndModifyStream to fail.

Original issue's description:
> Adding the ability to create an RtpSender without a track.
>
> This CL also changes AddStream to immediately create a sender, rather
> than waiting until the track is seen in SDP. And the PeerConnection now
> builds the list of "send streams" from the list of senders, rather than
> the collection of local media streams.
>
> Committed: https://crrev.com/ac9d92ccbe2b29590c53f702e11dc625820480d5
> Cr-Commit-Position: refs/heads/master@{#10414}

TBR=pthatcher@webrtc.org,pthatcher@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/8f46c63f6f764254892f4111b54aa1cc8f32eeeb
Cr-Commit-Position: refs/heads/master@{#10417}

[Taylor Brandstetter, 2015-10-26 21:10:55]

Created Revert of Adding the ability to create an RtpSender without a track.

[commit-bot: I haz the power, 2015-10-26 21:11:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1426443007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1426443007/1

[commit-bot: I haz the power, 2015-10-26 21:11:22]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-26 21:11:36]

Patchset 1 (id:??) landed as
https://crrev.com/8f46c63f6f764254892f4111b54aa1cc8f32eeeb
Cr-Commit-Position: refs/heads/master@{#10417}

[Taylor Brandstetter, 2015-11-09 22:36:24]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.webrtc.org/1413983004/ by deadbeef@webrtc.org.

The reason for reverting is: Relanding, after changing the expectations of
WebRtcBrowserTest.CallAndModifyStream..