Update mixer parameters logic

[foonerd]

Although the error seems to be harmless, debug level shows packets queue buildup over time on track or source change.

[volumio]

What if:

• We remove the option to set volume from mpd
• We don't populate that line

@foonerd

[foonerd]

I think we need a bit of impact testing with line removed.
Will share my findings from test.

[volumio]

AFAIK, this was used only if mpd was allowed to set the volume, which should be handled differently anyway (going trough Volumio)

[foonerd]

Well, together wit Marco we did further testing by commenting out this part completely or setting mixerstrings = mixerstrings
It seems to be snake oil.