remove gsm.mk
Revert "hammerhead: Enable offload for USB audio"

This reverts commit 084ce9d91a13ad840f5e3efcec6d6a8fd5c1f8b2.
Revert "hammerhead: Better USB audio support"

This reverts commit 231b33f34035ca09c5bf6580c81b658c75590485.
Revert "hammerhead: Enable USB audio"

This reverts commit 975d6fc7161b2d99e1d715db91a1aefba5298afa.