alsa-mixer: don't make lineout unavailable when headphones are plugged in

alsa-mixer: don't make lineout unavailable when headphones are plugged in

This reverts commit 66f97c35bda9524985b8d34d9a7dbfa9b1359df5. The commit
message was:

    alsa-mixer: Disable line-out if headphone jack is plugged

    Line-out gets muted when headphones are plugged in on HDA cards, encode
    this in the line-out path so pulse can match that state.

I don't think the mentioned auto-muting happens any more by default,
and some users want to use lineout while having headphones plugged in.

Fixes: https://gitlab.freedesktop.org/pulseaudio/pulseaudio/issues/583