Revert "vtenc: free input buffer ASAP"

This reverts commit 6101fc57b8.

GstVideoEncoder assumes that the input buffer is available until _finish_frame.

https://bugzilla.gnome.org/show_bug.cgi?id=756951

sys/applemedia/vtenc.c

@@ -1202,10 +1202,6 @@ gst_vtenc_encode_frame (GstVTEnc * self, GstVideoCodecFrame * frame)
         (int) vt_status);
   }
 
-  /* VTCompressionSessionEncodeFrame retained pbuf
-   * and we want to free input_buffer ASAP */
-  gst_buffer_replace (&frame->input_buffer, NULL);
-
   gst_video_codec_frame_unref (frame);
 
   CVPixelBufferRelease (pbuf);