Removes EncodedImageCallbackTestImpl and DecodedImageCallbackTestImpl in vp8_impl_unittest.cc. Bug: none Change-Id: If4a8d7ed5eb5834614e5c66f1b14f5c586c09b68 Reviewed-on: https://webrtc-review.googlesource.com/55640 Commit-Queue: Åsa Persson <asapersson@webrtc.org> Reviewed-by: Rasmus Brandt <brandtr@webrtc.org> Cr-Commit-Position: refs/heads/master@{#22435}