Remove hardcoded kValueSizeBytes values from variable-length header extensions.

webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc b/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
index 13f488b09a8a2416968e072854540746df600146..869e9b102e2c89ac1c68e89ba6088c9c4506eb12 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
@@ -246,7 +246,6 @@ bool VideoContentTypeExtension::Write(uint8_t* data,
 
 // RtpStreamId.
 constexpr RTPExtensionType RtpStreamId::kId;
-constexpr uint8_t RtpStreamId::kValueSizeBytes;
 constexpr const char* RtpStreamId::kUri;
 
 bool RtpStreamId::Parse(rtc::ArrayView<const uint8_t> data, StreamId* rsid) {
@@ -270,7 +269,6 @@ bool RtpStreamId::Parse(rtc::ArrayView<const uint8_t> data, std::string* rsid) {
 
 // RepairedRtpStreamId.
 constexpr RTPExtensionType RepairedRtpStreamId::kId;
-constexpr uint8_t RepairedRtpStreamId::kValueSizeBytes;
 constexpr const char* RepairedRtpStreamId::kUri;
 
 // RtpStreamId and RepairedRtpStreamId use the same format to store rsid.