ACM: Remove functions related to DTMF

ACM: Remove functions related to DTMF

The functions were essentially no-op. Also removing forward declaration
of ACMDTMFDetection, which was not used.

BUG=3520
Committed: https://crrev.com/061b79af6023b6caf9975be39fe53dd0ec3b7464
Cr-Commit-Position: refs/heads/master@{#9982}

[hlundin-webrtc, 2015-09-17 09:09:17]

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

[hlundin-webrtc, 2015-09-17 09:10:28]

Please, take a look.

kwiberg: all
henrikg: voice_engine

[Henrik Grunell WebRTC, 2015-09-17 09:52:33]

voice_engine lgtm

[kwiberg-webrtc, 2015-09-17 10:56:31]

lgtm

[hlundin-webrtc, 2015-09-17 13:33:48]

The CQ bit was checked by henrik.lundin@webrtc.org

[commit-bot: I haz the power, 2015-09-17 13:34:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1356543003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1356543003/1

[commit-bot: I haz the power, 2015-09-17 15:34:18]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-17 15:34:18]

Try jobs failed on following builders:
  android on tryserver.webrtc (JOB_TIMED_OUT, no build URL)
  win_drmemory_light on tryserver.webrtc (JOB_TIMED_OUT, no build URL)

[hlundin-webrtc, 2015-09-18 08:27:28]

The CQ bit was checked by henrik.lundin@webrtc.org

[commit-bot: I haz the power, 2015-09-18 08:27:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1356543003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1356543003/1

[commit-bot: I haz the power, 2015-09-18 08:29:16]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-18 08:29:23]

Patchset 1 (id:??) landed as
https://crrev.com/061b79af6023b6caf9975be39fe53dd0ec3b7464
Cr-Commit-Position: refs/heads/master@{#9982}