Delete unowned buffer in EncodedImage.

Bug: webrtc:9378
Change-Id: Ice48020c0f14905cbc185b52c88bbb9ac3bb4c93
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/128575
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33510}

modules/video_coding/codecs/multiplex/multiplex_encoder_adapter.cc

@@ -298,9 +298,6 @@ EncodedImageCallback::Result MultiplexEncoderAdapter::OnEncodedImage(
       PayloadStringToCodecType(associated_format_.name);
   image_component.encoded_image = encodedImage;
 
-  // If we don't already own the buffer, make a copy.
-  image_component.encoded_image.Retain();
-
   MutexLock lock(&mutex_);
   const auto& stashed_image_itr =
       stashed_images_.find(encodedImage.Timestamp());