Remove ScopedBytes use

The libnativehelper ScopedBytes class is being deprecated. It's use in
android_media_AudioTrack.cpp is unnecessary because the JNI method
takes a direct buffer as an argument whereas ScopedBytes classes exist
to mask the difference between byte arrays and byte buffers.

Bug: 119840313
Test: m -j32
Change-Id: I2a6478dbaa861c5391cc298871df0f8cd1f1439c