Revert of TransportController refactoring.

Revert of TransportController refactoring. (patchset #6 id:100001 of https://codereview.webrtc.org/1350523003/ )

Reason for revert:
This CL causes problems with the WebRTC-in-Chromium FYI bots. Presumably it needs to be done in several steps, where removed files are emptied instead of removed in the first step.

Original issue's description:
> TransportController refactoring.
>
> Getting rid of TransportProxy, and in its place adding a
> TransportController class which will facilitate access to and manage
> the lifetimes of Transports. These Transports will now be accessed
> solely from the worker thread, simplifying their implementation.
>
> This refactoring also pulls Transport-related code out of BaseSession.
> Which means that BaseChannels will now rely on the TransportController
> interface to create channels, rather than BaseSession.
>
> Committed: https://crrev.com/47ee2f3b9f33e8938948c482c921d4e13a3acd83
> Cr-Commit-Position: refs/heads/master@{#10022}

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

Committed: https://crrev.com/a81a42f584baa0d93a4b93da9632415e8922450c
Cr-Commit-Position: refs/heads/master@{#10024}

[torbjorng (webrtc), 2015-09-23 09:16:28]

Created Revert of TransportController refactoring.

[commit-bot: I haz the power, 2015-09-23 09:16:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1358413003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1358413003/1

[commit-bot: I haz the power, 2015-09-23 09:17:04]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-23 09:24:33]

Patchset 1 (id:??) landed as
https://crrev.com/a81a42f584baa0d93a4b93da9632415e8922450c
Cr-Commit-Position: refs/heads/master@{#10024}

[Taylor Brandstetter, 2015-09-23 18:37:45]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.webrtc.org/1361773005/ by deadbeef@webrtc.org.

The reason for reverting is: This CL just landed:
https://codereview.chromium.org/1323243006/

Which fixes the FYI bots for the original CL, and breaks them for this revert..