Move AudioDecoderIlbc next to AudioEncoderIlbc

Move AudioDecoderIlbc next to AudioEncoderIlbc

All AudioDecoder subclasses have historically lived in NetEq, but they
fit better with the codec they wrap.

BUG=webrtc:4557
Committed: https://crrev.com/fff9f176f542053ca7cb887c184c72ad3fc5755d
Cr-Commit-Position: refs/heads/master@{#9961}

[kwiberg-webrtc, 2015-09-16 12:26:29]

kwiberg@webrtc.org changed reviewers:
+ henrik.lundin@webrtc.org

[kwiberg-webrtc, 2015-09-16 12:26:42]

As noted elsewhere, this CL leads to the AudioDecoder subclass not being
excluded from the build when it should be, just as is already the case with the
AudioEncoder subclass and the codec's C implementation. I'll deal with tha
problem all at once in a future CL.

[hlundin-webrtc, 2015-09-16 12:40:05]

lgtm

[kwiberg-webrtc, 2015-09-17 04:24:53]

The CQ bit was checked by kwiberg@webrtc.org

[kwiberg-webrtc, 2015-09-17 04:24:53]

The patchset sent to the CQ was uploaded after l-g-t-m from
henrik.lundin@webrtc.org
Link to the patchset: https://codereview.webrtc.org/1348053002/#ps20001 (title:
"rebase")

[commit-bot: I haz the power, 2015-09-17 04:24:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1348053002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1348053002/20001

[commit-bot: I haz the power, 2015-09-17 04:26:37]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-17 04:26:48]

Patchset 2 (id:??) landed as
https://crrev.com/fff9f176f542053ca7cb887c184c72ad3fc5755d
Cr-Commit-Position: refs/heads/master@{#9961}