Removing unnecessary =default constructor for RtpPacketSendInfo.

This =default declaration has no effect other than to break designated
initialization in C++20 by making the type no longer an aggregate.

Bug: None
Change-Id: I20a4c285b7cbfed074291b9ee27c03aa29bada32
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/281960
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38573}
diff --git a/modules/rtp_rtcp/include/rtp_rtcp_defines.h b/modules/rtp_rtcp/include/rtp_rtcp_defines.h
index 1797b3e..c482e0c 100644
--- a/modules/rtp_rtcp/include/rtp_rtcp_defines.h
+++ b/modules/rtp_rtcp/include/rtp_rtcp_defines.h
@@ -231,9 +231,6 @@
 };
 
 struct RtpPacketSendInfo {
- public:
-  RtpPacketSendInfo() = default;
-
   uint16_t transport_sequence_number = 0;
   absl::optional<uint32_t> media_ssrc;
   uint16_t rtp_sequence_number = 0;  // Only valid if `media_ssrc` is set.