Removing DtlsIdentityService[Interface] which has been replaced by DtlsIdentityStore[Interface/Impl]

Removing DtlsIdentityService[Interface] which has been replaced by DtlsIdentityStore[Interface/Impl].

This is CL is part of an effort to land https://codereview.webrtc.org/1176383004 without breaking Chromium.
See bug for more information.

BUG=webrtc:4899
Committed: https://crrev.com/c558af854f5f14be49652b684d3e2c328fb071d7
Cr-Commit-Position: refs/heads/master@{#9705}

[hbos, 2015-08-13 12:04:12]

hbos@webrtc.org changed reviewers:
+ tommi@webrtc.org

[hbos, 2015-08-13 12:04:13]

PTAL tommi.

[tommi, 2015-08-13 12:53:39]

lgtm

[hbos, 2015-08-13 14:05:53]

The CQ bit was checked by hbos@webrtc.org

[commit-bot: I haz the power, 2015-08-13 14:05:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1282413002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1282413002/1

[commit-bot: I haz the power, 2015-08-13 15:29:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-13 15:29:14]

Patchset 1 (id:??) landed as
https://crrev.com/c558af854f5f14be49652b684d3e2c328fb071d7
Cr-Commit-Position: refs/heads/master@{#9705}