Remove libmad VERSION file

[feiyunw]

After upgrading to ndk r23b, the libmad VERSION file will conflict with the C++ library header file as many files have it included.

In file included from D:\android\android-sdk\ndk\23.1.7779620\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\c++\v1\cstddef:37:
D:\prj\openxcom-android\app\src\main\jni\libmad-0.15.1b\VERSION:1:1: error: expected unqualified-id

The branch is supposed to setup the test environment.