Remove more zombie small plugin code.
Remove more zombie small plugin code.

The LV2 helpers (mixins, event buffer iterator) are not needed anymore, and
don't even look like a good idea in retrospect. They may need to be rewritten
using different approach, if at all.

adiknoth/calf,jnetterf/calf,zamaudio/calf-LR4,zamaudio/calf-LR4,adiknoth/calf,adiknoth/calf,zamaudio/calf-LR4,zamaudio/calf-LR4,jnetterf/calf,jnetterf/calf,zamaudio/calf-LR4,jnetterf/calf,adiknoth/calf,adiknoth/calf,jnetterf/calf