Remove VCM_*_PAYLOAD_TYPE constants.

These payload types aren't directly connected to any payload type, and
the payload type still has to be negotiated externally. As such these
constants are just a source of confusion.

BUG=
R=stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1215603003

Cr-Commit-Position: refs/heads/master@{#9546}

webrtc/modules/video_coding/main/interface/video_coding_defines.h

@@ -36,13 +36,6 @@ namespace webrtc {
 #define VCM_ERROR_REQUEST_SLI   -12
 #define VCM_NOT_IMPLEMENTED     -20
 
-#define VCM_RED_PAYLOAD_TYPE        96
-#define VCM_ULPFEC_PAYLOAD_TYPE     97
-#define VCM_VP8_PAYLOAD_TYPE       100
-#define VCM_VP9_PAYLOAD_TYPE       101
-#define VCM_I420_PAYLOAD_TYPE      124
-#define VCM_H264_PAYLOAD_TYPE      127
-
 enum { kDefaultStartBitrateKbps = 300 };
 
 enum VCMVideoProtection {