Reland "Move rtp-specific config out of EncoderSettings."

This is a reland of bc900cb1d1810fcf678fe41cf1e3966daa39c88c

Original change's description:
> Move rtp-specific config out of EncoderSettings.
> 
> In VideoSendStream::Config, move payload_name and payload_type from
> EncoderSettings to Rtp.
> 
> EncoderSettings now contains configuration for VideoStreamEncoder only,
> and should perhaps be renamed in a follow up cl. It's no longer
> passed as an argument to VideoCodecInitializer::SetupCodec.
> 
> The latter then needs a different way to know the codec type,
> which is provided by a new codec_type member in VideoEncoderConfig.
> 
> Bug: webrtc:8830
> Change-Id: Ifcc691aef1ee6a95e43c0452c5e630d92a511cd6
> Reviewed-on: https://webrtc-review.googlesource.com/62062
> Commit-Queue: Niels Moller <nisse@webrtc.org>
> Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
> Reviewed-by: Stefan Holmer <stefan@webrtc.org>
> Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#22532}

Bug: webrtc:8830
Change-Id: If88ef7d57cdaa4fae3c7b2a97ea5a6e1b833e019
Reviewed-on: https://webrtc-review.googlesource.com/63721
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22595}
diff --git a/modules/video_coding/video_codec_initializer.cc b/modules/video_coding/video_codec_initializer.cc
index 02c0c4a..892113b 100644
--- a/modules/video_coding/video_codec_initializer.cc
+++ b/modules/video_coding/video_codec_initializer.cc
@@ -26,23 +26,15 @@
 
 bool VideoCodecInitializer::SetupCodec(
     const VideoEncoderConfig& config,
-    const VideoSendStream::Config::EncoderSettings settings,
     const std::vector<VideoStream>& streams,
     bool nack_enabled,
     VideoCodec* codec,
     std::unique_ptr<VideoBitrateAllocator>* bitrate_allocator) {
-  VideoCodecType codec_type = config.codec_type;
-  // TODO(nisse): Transition hack, the intention is to delete the
-  // |settings| argument and require configuration via
-  // config.codec_type.
-  if (codec_type == kVideoCodecUnknown) {
-    codec_type = PayloadStringToCodecType(settings.payload_name);
-  }
-  if (codec_type == kVideoCodecMultiplex) {
+  if (config.codec_type == kVideoCodecMultiplex) {
     VideoEncoderConfig associated_config = config.Copy();
     associated_config.codec_type = kVideoCodecVP9;
-    if (!SetupCodec(associated_config, settings /* ignored */, streams,
-                    nack_enabled, codec, bitrate_allocator)) {
+    if (!SetupCodec(associated_config, streams, nack_enabled, codec,
+                    bitrate_allocator)) {
       RTC_LOG(LS_ERROR) << "Failed to create stereo encoder configuration.";
       return false;
     }
@@ -51,7 +43,7 @@
   }
 
   *codec =
-      VideoEncoderConfigToVideoCodec(config, streams, codec_type, nack_enabled);
+      VideoEncoderConfigToVideoCodec(config, streams, nack_enabled);
   *bitrate_allocator = CreateBitrateAllocator(*codec);
 
   return true;
@@ -77,7 +69,6 @@
 VideoCodec VideoCodecInitializer::VideoEncoderConfigToVideoCodec(
     const VideoEncoderConfig& config,
     const std::vector<VideoStream>& streams,
-    VideoCodecType codec_type,
     bool nack_enabled) {
   static const int kEncoderMinBitrateKbps = 30;
   RTC_DCHECK(!streams.empty());
@@ -85,7 +76,7 @@
 
   VideoCodec video_codec;
   memset(&video_codec, 0, sizeof(video_codec));
-  video_codec.codecType = codec_type;
+  video_codec.codecType = config.codec_type;
 
   switch (config.content_type) {
     case VideoEncoderConfig::ContentType::kRealtimeVideo: