Revert "rtpbin: receive bundle support"
This reverts commit dcd3ce97. This functionality was implemented for gstopenwebrtc, but it turned out this was not actually needed for webrtc bundling support, as shown in webrtcbin. It also doesn't correspond to any standards. This is an API break, but nothing should actually depend on this, at least not for its initial purpose. Changes in rtpbin.c were reverted manually, to preserve some refactoring that had occurred in the original commit. Fixes #537