audio/muse: Deprecate

• MuSE randomly crashes and hangs at runtime
• It is unmaintained upstream for ~8 years now
• It does not build with Clang 6 [1]

[1] http://beefy12.nyi.freebsd.org/data/head-amd64-default/p461678_s329188/logs/MuSE-0.9.2_16.log