Remove old FakeVP8Encoder alias.

Bug: None
Change-Id: I834a9caad49d47898b826e6be491f663445b6b44
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169856
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Commit-Queue: Nikita Zetilov <zetilovn@google.com>
Cr-Commit-Position: refs/heads/master@{#30716}

test/fake_vp8_encoder.h

@@ -70,7 +70,6 @@ class FakeVp8Encoder : public FakeEncoder {
   std::unique_ptr<Vp8FrameBufferController> frame_buffer_controller_
       RTC_GUARDED_BY(sequence_checker_);
 };
-using FakeVP8Encoder = FakeVp8Encoder;
 
 }  // namespace test
 }  // namespace webrtc