Revert "Disable the test: DtmfTest.ManualSuccessfullySendsIn/OutOfBandTelephoneEvents"
Revert "Disable the test: DtmfTest.ManualSuccessfullySendsIn/OutOfBandTelephoneEvents"

This reverts commit r5479.

R=henrika@webrtc.org
BUG=2880

Review URL: https://webrtc-codereview.appspot.com/7989004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 3e6c41c48f4fbbc226892bd7946a2073d8a8a523

sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc