media: Remove unused type aliases in MediaCodecLoop

This is part of the base::Callback migration.

Context: https://cs.chromium.org/chromium/src/docs/callback.md?rcl=9fcc3764aea8f97e9f6de4a9ee61d554e67edcda&l=40

Bug: 714018
Change-Id: Ic6d5627e79a10a86e1fe3847494b2ca45b60ff06
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2047246
Commit-Queue: Jose Lopes <jabolopes@google.com>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743468}

media/base/android/media_codec_loop.h

@@ -107,10 +107,6 @@ namespace media {
 
 class MEDIA_EXPORT MediaCodecLoop {
  public:
-  // TODO(liberato): this exists in video_decoder.h and audio_decoder.h too.
-  using InitCB = base::Callback<void(bool success)>;
-  using DecodeCB = base::Callback<void(DecodeStatus status)>;
-
   // Data that the client wants to put into an input buffer.
   struct InputData {
     InputData();