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

Unfetchable and abandoned upstream in 2003
Reference: https://www.nue.tu-berlin.de/menue/mitarbeiterinnen/ehemalige_mitarbeiterinnen/tilman_liebchen/lpac_lossless_audio_codec_for_windows_and_linux/

PR: 258641
Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D32041