Relanding: Remove the IceTransportInternal2.

Introduing IceTransportInternal2 is a temporary fix to switch the base
class of P2PTransportChannel to IceTransportInternal without breaking
Chromium. It is removed in this CL.

Reland this CL after Chromium doesn't depend on this.

BUG=webrtc:6951

Review-Url: https://codereview.webrtc.org/2632563002
Review-Url: https://codereview.webrtc.org/2632563002
Cr-Original-Commit-Position: refs/heads/master@{#16960}
Committed: https://chromium.googlesource.com/external/webrtc/+/c7953fa716dc26db1123bb80351d46e496792c81
Cr-Original-Original-Commit-Position: refs/heads/master@{#16131}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 2c48d0c5313dee5dd5fe846eaf660cc7fa901659
diff --git a/p2p/base/icetransportinternal.h b/p2p/base/icetransportinternal.h
index 074a34a..e9b40dc 100644
--- a/p2p/base/icetransportinternal.h
+++ b/p2p/base/icetransportinternal.h
@@ -26,9 +26,6 @@
 
 namespace cricket {
 
-class IceTransportInternal;
-typedef IceTransportInternal IceTransportInternal2;
-
 // TODO(zhihuang): Replace this with
 // PeerConnectionInterface::IceConnectionState.
 enum class IceTransportState {