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 #3 id:300001 of https://codereview.webrtc.org/1413983004/ )

Reason for revert:
Still breaking CallAndModifyStream. Chromium CL intended to fix it (https://codereview.chromium.org/1435713002/) wasn't sufficient, because I forgot to call addStream/removeStream on the second connection.

Original issue's description:
> Reland of Adding the ability to create an RtpSender without a track. (patchset #1 id:1 of https://codereview.webrtc.org/1426443007/ )
>
> Reason for revert:
> Relanding, after changing the expectations of WebRtcBrowserTest.CallAndModifyStream.
>
> Original issue's description:
> > 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}
>
> TBR=pthatcher@webrtc.org,pthatcher@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
>
> Committed: https://crrev.com/6834fa10f142bf5e2275142acb834898911d09ae
> Cr-Commit-Position: refs/heads/master@{#10730}

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

Committed: https://crrev.com/5def7b9fdea0d027bca3df734d86fb877a83bdbf
Cr-Commit-Position: refs/heads/master@{#10732}

[Taylor Brandstetter, 2015-11-20 19:42:58]

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

[commit-bot: I haz the power, 2015-11-20 19:43:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1460323002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1460323002/1

[commit-bot: I haz the power, 2015-11-20 19:43:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-20 19:43:36]

Patchset 1 (id:??) landed as
https://crrev.com/5def7b9fdea0d027bca3df734d86fb877a83bdbf
Cr-Commit-Position: refs/heads/master@{#10732}

[Taylor Brandstetter, 2015-11-23 17:53:31]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.webrtc.org/1468113002/ by deadbeef@webrtc.org.

The reason for reverting is: Relanding again, after fixing CallAndModifyStream
again..