This commit also modifies build-aux to update libdatachannel.
This commit also modifies obs-webrtc to avoid a compiler error.
Notable changes:
* deps.ffmpeg: Update libdatachannel to 0.20.1
* deps.macos: Remove Carla
* deps.macos: Add uthash to macOS deps
* deps.windows: Remove Carla
* deps.windows: Add uthash to Windows deps