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.

BUG=webrtc:6951

Review-Url: https://codereview.webrtc.org/2632563002
Cr-Original-Commit-Position: refs/heads/master@{#16083}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 8aaa51190e043e12b7a9acb28ff730e575d651ae
1 file changed