Remove unused audio mk files

These are empty and useless.

Change-Id: I23cd1be105f7bddbf555a35e10efcc92a7c1eb47
Merge branch 'cm-11.0' of git://github.com/CyanogenMod/android_vendor_cm into HEAD
Merge branch 'pixel-4.4' of github.com:PixelROM/android_vendor_cm into pixel-4.4