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/encoded_frame.h

@@ -52,7 +52,6 @@ class RTC_EXPORT VCMEncodedFrame : public EncodedImage {
   using EncodedImage::GetEncodedData;
   using EncodedImage::NtpTimeMs;
   using EncodedImage::PacketInfos;
-  using EncodedImage::Retain;
   using EncodedImage::set_size;
   using EncodedImage::SetColorSpace;
   using EncodedImage::SetEncodedData;