Delete RTPReceiverStrategy::OnNewPayloadTypeCreated and related code.

Bug: webrtc:7135
Change-Id: Ic20d98cbfb8154f5abbc2501cbcccb950148e732
Reviewed-on: https://webrtc-review.googlesource.com/92396
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24219}

modules/rtp_rtcp/include/rtp_rtcp_defines.h

@@ -89,8 +89,6 @@ class PayloadUnion {
   absl::variant<AudioPayload, VideoPayload> payload_;
 };
 
-enum RTPAliveType { kRtpDead = 0, kRtpNoRtp = 1, kRtpAlive = 2 };
-
 enum ProtectionType { kUnprotectedPacket, kProtectedPacket };
 
 enum StorageType { kDontRetransmit, kAllowRetransmission };