Delete payload_type from VCMEncoderDatabase and vcm::VideoSender.

Bug: webrtc:8830
Change-Id: Ie6a874023618a5540e138b34edfcad1ce6e8d391
Reviewed-on: https://webrtc-review.googlesource.com/62102
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22474}

modules/video_coding/video_coding_impl.cc

@@ -126,9 +126,9 @@ class VideoCodingModuleImpl : public VideoCodingModule {
   }
 
   int32_t RegisterExternalEncoder(VideoEncoder* externalEncoder,
-                                  uint8_t payloadType,
+                                  uint8_t /* payloadType */,
                                   bool internalSource) override {
-    sender_.RegisterExternalEncoder(externalEncoder, payloadType,
+    sender_.RegisterExternalEncoder(externalEncoder,
                                     internalSource);
     return 0;
   }