Revert of Replacing DtlsIdentityStoreInterface with RTCCertificateGeneratorInterface. (patchset #2 id:20001 of https://codereview.webrtc.org/2013523002/ )

Reason for revert:
There are more CreatePeerConnection calls than I anticipated/had found in Chromium, like remoting/protocol/webrtc_transport.cc. Reverting due to broken Chromium FYI bots.

Original issue's description:
> Replacing DtlsIdentityStoreInterface with RTCCertificateGeneratorInterface.
>
> The store was used in WebRtcSessionDescriptionFactory to generate certificates,
> now a generator is used instead (new API). PeerConnection[Factory][Interface],
> and WebRtcSession are updated to pass generators all the way down to the
> WebRtcSessionDescriptionFactory instead of stores.
>
> The webrtc implementation of a generator, RTCCertificateGenerator, is used as
> the default generator (peerconnectionfactory.cc:189) instead of the webrtc
> implementation of a store, DtlsIdentityStoreImpl.
>   The generator is fully parameterized and does not generate RSA-1024 unless you
> ask for it (which makes sense not to do beforehand since ECDSA is now default).
> The store was not fully parameterized (known filed bug).
>
> The "top" layer, PeerConnectionFactoryInterface::CreatePeerConnection, is
> updated to take a generator instead of a store. But as to not break Chromium,
> the old function signature taking a store is kept. It is implemented to invoke
> the generator version by wrapping the store in an
> RTCCertificateGeneratorStoreWrapper. As soon as Chromium is updated to use the
> new function signature we can remove the old CreatePeerConnection.
>   Due to having multiple CreatePeerConnection signatures, some calling places
> are updated to resolve the ambiguity introduced.
>
> BUG=webrtc:5707, webrtc:5708
> R=phoglund@webrtc.org, tommi@webrtc.org
> TBR=tkchin@webrc.org
>
> Committed: https://chromium.googlesource.com/external/webrtc/+/400781a2091d09a725b32c6953247036b22478e8

TBR=tkchin@webrtc.org,tommi@webrtc.org,phoglund@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:5707, webrtc:5708

Review-Url: https://codereview.webrtc.org/2020633002
Cr-Commit-Position: refs/heads/master@{#12948}
diff --git a/webrtc/api/peerconnectioninterface.h b/webrtc/api/peerconnectioninterface.h
index caa6b31..4fa9bf2 100644
--- a/webrtc/api/peerconnectioninterface.h
+++ b/webrtc/api/peerconnectioninterface.h
@@ -68,7 +68,6 @@
 #include "webrtc/base/fileutils.h"
 #include "webrtc/base/network.h"
 #include "webrtc/base/rtccertificate.h"
-#include "webrtc/base/rtccertificategenerator.h"
 #include "webrtc/base/socketaddress.h"
 #include "webrtc/base/sslstreamadapter.h"
 #include "webrtc/media/base/mediachannel.h"
@@ -581,48 +580,14 @@
       const PeerConnectionInterface::RTCConfiguration& configuration,
       const MediaConstraintsInterface* constraints,
       std::unique_ptr<cricket::PortAllocator> allocator,
-      std::unique_ptr<rtc::RTCCertificateGeneratorInterface> cert_generator,
-      PeerConnectionObserver* observer) = 0;
-  // TODO(hbos): To be removed in favor of the |cert_generator| version as soon
-  // as Chromium stops using this version. See bugs.webrtc.org/5707,
-  // bugs.webrtc.org/5708.
-  rtc::scoped_refptr<PeerConnectionInterface> CreatePeerConnection(
-      const PeerConnectionInterface::RTCConfiguration& configuration,
-      const MediaConstraintsInterface* constraints,
-      std::unique_ptr<cricket::PortAllocator> allocator,
       std::unique_ptr<DtlsIdentityStoreInterface> dtls_identity_store,
-      PeerConnectionObserver* observer) {
-    return CreatePeerConnection(
-        configuration,
-        constraints,
-        std::move(allocator),
-        std::unique_ptr<rtc::RTCCertificateGeneratorInterface>(
-            dtls_identity_store ? new RTCCertificateGeneratorStoreWrapper(
-                std::move(dtls_identity_store)) : nullptr),
-        observer);
-  }
+      PeerConnectionObserver* observer) = 0;
 
   virtual rtc::scoped_refptr<PeerConnectionInterface> CreatePeerConnection(
       const PeerConnectionInterface::RTCConfiguration& configuration,
       std::unique_ptr<cricket::PortAllocator> allocator,
-      std::unique_ptr<rtc::RTCCertificateGeneratorInterface> cert_generator,
-      PeerConnectionObserver* observer) = 0;
-  // TODO(hbos): To be removed in favor of the |cert_generator| version as soon
-  // as Chromium stops using this version. See bugs.webrtc.org/5707,
-  // bugs.webrtc.org/5708.
-  rtc::scoped_refptr<PeerConnectionInterface> CreatePeerConnection(
-      const PeerConnectionInterface::RTCConfiguration& configuration,
-      std::unique_ptr<cricket::PortAllocator> allocator,
       std::unique_ptr<DtlsIdentityStoreInterface> dtls_identity_store,
-      PeerConnectionObserver* observer) {
-    return CreatePeerConnection(
-        configuration,
-        std::move(allocator),
-        std::unique_ptr<rtc::RTCCertificateGeneratorInterface>(
-            dtls_identity_store ? new RTCCertificateGeneratorStoreWrapper(
-                std::move(dtls_identity_store)) : nullptr),
-        observer);
-  }
+      PeerConnectionObserver* observer) = 0;
 
   virtual rtc::scoped_refptr<MediaStreamInterface>
       CreateLocalMediaStream(const std::string& label) = 0;