remove persistence from EffectUnit routing switches

[Be-ing]

I thought this would be useful before when I worked on #1103, but experience has shown it is annoying. I want effect unit 1 assigned to deck 2, unit 2 to deck 2, unit 3 to deck 3, and unit 4 to deck 4 on startup regardless of how the routing switches happened to be when I last shut down Mixxx.

[daschuer]

Can we make this optional. If we think on the broadcasting use case, where mic and master effects are needed, it could be annoying to adjust the routing on every startup.

[ronso0]

I'm mostly using 2 decks and I try to work with two different effect chains for each deck, which is now easy to handle with components-js. It would be nice if the assignment would persist after restart. Also, assignment is easy to see and to change with the in-deck FX buttons you suggested.

[Be-ing]

Hmm, a preference option may be warranted then. I'll return to this after #1377 is merged.

[JosepMaJAZ]

Talking about persistence...
I do not find it annyoing that the routing is persisted (Although it's reasonable to have the option to reset them on startup too), but what I do find annoying is to have to reenable the effects inside the effect unit each time.
My mapping currently controls the routing, and I don't have individual effect buttons on my controller. I could change the setup to control two effects on each effectrack, but then I would need the routing to be persisted.