Delete VideoCodec::plType member

Followup to https://webrtc-review.googlesource.com/c/src/+/181201.

Bug: None
Change-Id: Ia7e2a924d2a192472f4a9cd2572e3443a313e41a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/181370
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31929}

api/video_codecs/video_codec.h

@@ -103,9 +103,6 @@ class RTC_EXPORT VideoCodec {
 
   // Public variables. TODO(hta): Make them private with accessors.
   VideoCodecType codecType;
-  // TODO(nisse): Unused in webrtc, delete as soon as downstream projects are
-  // updated.
-  unsigned char plType;
 
   // TODO(nisse): Change to int, for consistency.
   uint16_t width;