This is one less DtlsIdentityStoreInterface implementation, and one step closer to removing this interface in favor of RTCCertificateGeneratorInterface. This also removes PeerConnectionInterface::CreatePeerConnectionWithStore which is no longer needed. BUG=webrtc:5707, webrtc:5708 R=tommi@webrtc.org Review URL: https://codereview.webrtc.org/2020623002 . Cr-Commit-Position: refs/heads/master@{#12990}