multimedia/QtAV: Mark DEPRECATED

QtAV is broken with FFmpeg 6.x and has been abandoned by the original
author [1]. The last release was 6 years ago.

No ports depend on this, so EXPIRATION_DATE has been set to one month
from now.

[1] https://github.com/wang-bin/QtAV/issues/1426#issuecomment-1538309106