Reland "Start supporting H264 packetization mode 0."

This is a reland of 3409cfa378e75c0c08d900e0848147929249a62b

Needed to change RtpVideoStreamReceiver to stop deregistering a payload
type if two payload types refer to the same codec (which now happens,
with the packetization mode 0/1 payload types). It's not clear why this
was being done in the first place.

Original change's description:
> Start supporting H264 packetization mode 0.
>
> The work was already done to support it, but it wasn't being negotiated
> in SDP.
>
> This means we'll now see 8 H264 payload types instead of 4; one for each
> combination of BP/CBP profiles, packetization modes 0/1, and RTX/non-RTX.
> This could be problematic in the future, since we're starting to run
> out of dynamic payload types (using 25 of 32).
>
> Bug: chromium:600254
> Change-Id: Ief2340db77c796f12980445b547b87e939170fae
> Reviewed-on: https://webrtc-review.googlesource.com/77264
> Commit-Queue: Taylor Brandstetter <deadbeef@webrtc.org>
> Reviewed-by: Erik Språng <sprang@webrtc.org>
> Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#23372}

Bug: chromium:600254
Change-Id: Ice1acc05acd1543d9b46e918de2bba0694d86259
Reviewed-on: https://webrtc-review.googlesource.com/78399
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23494}

modules/rtp_rtcp/include/rtp_payload_registry.h

@@ -41,11 +41,6 @@ class RTPPayloadRegistry {
 
   int32_t DeRegisterReceivePayload(int8_t payload_type);
 
-  int32_t ReceivePayloadType(const SdpAudioFormat& audio_format,
-                             int8_t* payload_type) const;
-  int32_t ReceivePayloadType(const VideoCodec& video_codec,
-                             int8_t* payload_type) const;
-
   int GetPayloadTypeFrequency(uint8_t payload_type) const;
 
   rtc::Optional<RtpUtility::Payload> PayloadTypeToPayload(