Turning FakeDtlsIdentityStore into FakeRTCCertificateGenerator.

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}
diff --git a/webrtc/api/api_tests.gyp b/webrtc/api/api_tests.gyp
index e58fdbc..b9778a3 100644
--- a/webrtc/api/api_tests.gyp
+++ b/webrtc/api/api_tests.gyp
@@ -51,8 +51,8 @@
         'test/fakeaudiocapturemodule_unittest.cc',
         'test/fakeconstraints.h',
         'test/fakedatachannelprovider.h',
-        'test/fakedtlsidentitystore.h',
         'test/fakeperiodicvideocapturer.h',
+        'test/fakertccertificategenerator.h',
         'test/fakevideotrackrenderer.h',
         'test/mockpeerconnectionobservers.h',
         'test/peerconnectiontestwrapper.h',