Reverses check for adding RTX to a codec. With this change RTX will
be added to external codecs.
Bug: webrtc:9516
Change-Id: Ie60b0b629dd9b05cbf20b2799bbf9bdccd8a6bcf
Reviewed-on: https://webrtc-review.googlesource.com/88441
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23962}