Revert "Delete VideoCodec::plName"
Revert "Delete VideoCodec::plName"

This reverts commit 89d88c0b9d61975bc63623ab8028377d8f9733dc.

Reason for revert: Breaks an internal project.

Original change's description:
> Delete VideoCodec::plName
> 
> All use was deleted in cl https://webrtc-review.googlesource.com/56100, now
> delete the actual member too.
> 
> Bug: webrtc:8830
> Change-Id: Iabbfd8eb08078e39a8e57f33f7c6a9de4bc3b6cb
> Reviewed-on: https://webrtc-review.googlesource.com/60300
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Commit-Queue: Niels Moller <0057859e47d61d90529d0f66d9ef692cefedb46a@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#22353}

TBR=kwiberg@webrtc.org,0057859e47d61d90529d0f66d9ef692cefedb46a@webrtc.org

Change-Id: I4901d2a7ef6de5f87520d7026906608904cf825e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:8830
Reviewed-on: https://webrtc-review.googlesource.com/60901
Reviewed-by: Niels Moller <0057859e47d61d90529d0f66d9ef692cefedb46a@webrtc.org>
Commit-Queue: Niels Moller <0057859e47d61d90529d0f66d9ef692cefedb46a@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#22363}
TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc