audio/mpiosh: Deprecate and set expiration date to 2021-12-31

Abandoned upstream, no new release since 2004
Supported battery powered media (MP3) players are over 15y old by
now and ranging between 64-512Mbyte in storage capacity

PR: 258644
Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D32046