Remove usage of RTPSender::SetSsrc() in unit tests
Remove usage of RTPSender::SetSsrc() in unit tests

That method will be retired, but some new tests managed to sneak in
usage again.

Bug: webrtc:10774
Change-Id: I354b4f5193625c8ddc75d54a252360810c3f60c8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/146983
Reviewed-by: Florent Castelli <238c27192d78679c9b4e4a6413f53bb164e8bb18@webrtc.org>
Commit-Queue: Erik Språng <3ab8c90c99d6dd7822e0fad803ab0211dd287ae5@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#28697}

ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc