* Remove fields no longer used, or that can be replaced by smaller code * Rename "channels" to a more meaningful "input pads" * Directly handle/use combiner pads in the combiners instead of on the playbin3 main structure Remove the corresponding combiner sinkpad whenever a uridecodebin3 source pad goes away * If used, store the corresponding combiner sink pad in the SourcePad helper structure Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2384>