Due to a limitation of RTCStatsMember<T> not supporting enums, as well as the fact that in JavaScript enums are represented as basic strings, the stats enums have always been represented by T=std::string. Now that we have WebIDL-ified[1] all RTCStats dictionaries and enum values are simply string-copied (example: [2]) it seems safe to assume that "stats enums are just strings" is here to stay. Therefore there is little value in having C++ structs that look like enums so I'm deleting those in favor of std::string operator==() comparisons, e.g. `if (rtp_stream.kind == "audio")`. This removes some lines of code from our code base. I mostly want to get rid of these because they were taking up about 20% of the rtcstats_objects.h real estate... [1] https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/modules/peerconnection/rtc_stats_report.idl [2] https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/modules/peerconnection/rtc_stats_report.cc;l=667;drc=cf34e84c9df94256abfb1716ba075ed203975755 Bug: webrtc:15245 Change-Id: Iaf0827d7aecebc1cc02976a61663d5298d684f07 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/308680 Commit-Queue: Henrik Boström <hbos@webrtc.org> Reviewed-by: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/main@{#40295}