Revert of Work on flexible mode and screen sharing.

Revert of Work on flexible mode and screen sharing. (patchset #28 id:520001 of https://codereview.webrtc.org/1328113004/ )

Reason for revert:
Seems to break VideoSendStreamTest.ReconfigureBitratesSetsEncoderBitratesCorrectly on Linux Memcheck buildbot.

Original issue's description:
> Work on flexible mode and screen sharing.
>
> Implement VP8 style screensharing but with spatial layers.
> Implement flexible mode.
>
> Files from other patches:
> generic_encoder.cc
> layer_filtering_transport.cc
>
> BUG=webrtc:4914
>
> Committed: https://crrev.com/77ccfb4d16c148e61a316746bb5d9705e8b39f4a
> Cr-Commit-Position: refs/heads/master@{#10572}

TBR=sprang@webrtc.org,stefan@webrtc.org,philipel@google.com,asapersson@webrtc.org,mflodman@webrtc.org,philipel@webrtc.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:4914
Committed: https://crrev.com/0be8f1d347bdb171462df89c2a4c69b3f3eb7519
Cr-Commit-Position: refs/heads/master@{#10578}

[terelius, 2015-11-10 13:30:55]

Created Revert of Work on flexible mode and screen sharing.

[commit-bot: I haz the power, 2015-11-10 13:31:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1438543002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1438543002/1

[commit-bot: I haz the power, 2015-11-10 13:31:22]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-10 13:31:33]

Patchset 1 (id:??) landed as
https://crrev.com/0be8f1d347bdb171462df89c2a4c69b3f3eb7519
Cr-Commit-Position: refs/heads/master@{#10578}

[philipel1, 2015-11-10 14:57:43]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.webrtc.org/1432553008/ by philipel@google.com.

The reason for reverting is: Failed test not related to this CL (test fails on
master at an earlier date), re-landing original CL..

[philipel, 2015-11-10 15:17:07]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.webrtc.org/1431283002/ by philipel@webrtc.org.

The reason for reverting is: Failed test not related to this CL (test fails on
master at an earlier date), re-landing original CL..

(This time from my @webrtc account.).