Tweak1/2 control bar displays are stale after clearing a MIDI binding

[sastraxi]

Steps to reproduce

1. Open up the pedalboard in http://pistomp.local
2. MIDI learn a parameter to Tweak1/2
3. Note that the display now shows the value and you can select it. Everything is in sync
4. Now remove the MIDI mapping in MOD-UI

Expected

The display of the control should go back to being grey with "none" text; the parameter should now be unbound and no longer show the parameter dialog when rotated. Fixed when you go to another pedalboard and back to this one

Actual

The control appears to be bound, and continues sending the MIDI messages. The parameter value drifts from the real one in MOD, which is correctly unchanged.

[sastraxi]

@jpremill take a look at this one if you're looking for low-hanging fruit!

[jpremill]

I'll look into it