Replace RelayPort with TurnPort in p2ptransportchannel tests.
Replace RelayPort with TurnPort in p2ptransportchannel tests.

Also remove the relay servers in the tests.
Most of the code and the downstream apps are using TurnPort, not RelayPort. Most of the tests in this file are not using RelayPort anyway.

BUG=None
R=deadbeef@webrtc.org

Review URL: https://codereview.webrtc.org/2380923002 .

Committed: https://crrev.com/c8d21712dde64c7d613d1ea56c840438505a909f
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#14441}
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#14446}

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