Prepare for deleting VideoCodec::plType

Deletes all webrtc usage of this member. Next step is to delete
any downstream references, and when that's done, the member can be
deleted.

Bug: None
Change-Id: I3f3a94a063dccf56468a1069653efd3809875b01
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/181201
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31911}

modules/video_coding/utility/simulcast_test_fixture_impl.cc

@@ -223,8 +223,6 @@ void SimulcastTestFixtureImpl::DefaultSettings(
   RTC_CHECK(settings);
   memset(settings, 0, sizeof(VideoCodec));
   settings->codecType = codec_type;
-  // 96 to 127 dynamic payload types for video codecs
-  settings->plType = 120;
   settings->startBitrate = 300;
   settings->minBitrate = 30;
   settings->maxBitrate = 0;