provisional processor control-box tweaks - possible fix for #6519

provisional processor control-box tweaks - possible fix for #6519

ControlBoxes are created/destroyed regularly (plugin re-order,
track selection -> Editor Mixer,...).

Properly disconnect the timer signal in the dtor and skip updateing the
tooltip unnecessarily (duplicate calls, Changed & Timer).

This should really be undone, the timer needs to be removed and Changed() used throughout.