Revert "Refactor AudioTrack callback to Interface"

This reverts commit f86d269d7cd4141129d2f4b18035e133324c15b7.

Reason for revert: Bug: 204055298

Change-Id: Ib48e22cce572845192f1a9bc4b2c70c4816fbe5a
diff --git a/media/libaaudio/src/legacy/AudioStreamTrack.cpp b/media/libaaudio/src/legacy/AudioStreamTrack.cpp
index fe84ec5..b512b48 100644
--- a/media/libaaudio/src/legacy/AudioStreamTrack.cpp
+++ b/media/libaaudio/src/legacy/AudioStreamTrack.cpp
@@ -103,7 +103,7 @@
             : getFormat();
 
     // Setup the callback if there is one.
-    AudioTrack::legacy_callback_t callback = nullptr;
+    AudioTrack::callback_t callback = nullptr;
     void *callbackData = nullptr;
     // Note that TRANSFER_SYNC does not allow FAST track
     AudioTrack::transfer_type streamTransferType = AudioTrack::transfer_type::TRANSFER_SYNC;