Remove DtlsIdentityStoreInterface, it is no longer used.

webrtc/api/BUILD.gn

 # Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("../build/webrtc.gni")
 import("//testing/test.gni")
@@ skipping 18 matching lines @@
 }
 
 source_set("libjingle_peerconnection") {
   cflags = []
   sources = [
     "audiotrack.cc",
     "audiotrack.h",
     "datachannel.cc",
     "datachannel.h",
     "datachannelinterface.h",
-    "dtlsidentitystore.h",
     "dtmfsender.cc",
     "dtmfsender.h",
     "dtmfsenderinterface.h",
     "jsep.h",
     "jsepicecandidate.cc",
     "jsepicecandidate.h",
     "jsepsessiondescription.cc",
     "jsepsessiondescription.h",
     "localaudiosource.cc",
     "localaudiosource.h",
@@ skipping 341 matching lines @@
       "../pc:rtc_pc",
       "../system_wrappers:metrics_default",
       "//testing/gmock",
     ]
 
     if (is_android) {
       deps += [ "//testing/android/native_test:native_test_support" ]
     }
   }
 }