Delete redundant mutation on EncodedImage in RTCVideoDecoderAdapterTest

Was missed in
https://chromium-review.googlesource.com/c/chromium/src/+/1862449, and
needed for relanding of webrtc cl
https://webrtc-review.googlesource.com/c/src/+/185122

Bug: webrtc:9378
Change-Id: I73e4203795c6879f989ac2fc722848db55f89ce3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2434926
Commit-Queue: Niels Möller <nisse@chromium.org>
Commit-Queue: Henrik Boström <hbos@chromium.org>
Auto-Submit: Niels Möller <nisse@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811184}

third_party/blink/renderer/platform/peerconnection/rtc_video_decoder_adapter_test.cc

@@ -222,8 +222,6 @@ class RTCVideoDecoderAdapterTest : public ::testing::Test {
     static const uint8_t data[1] = {0};
     input_image.SetEncodedData(
         webrtc::EncodedImageBuffer::Create(data, sizeof(data)));
-    input_image.set_size(1);
-    input_image.data()[0] = 0;
     input_image._completeFrame = true;
     input_image._frameType = webrtc::VideoFrameType::kVideoFrameKey;
     input_image.SetTimestamp(timestamp);