eliminate some hacky primitive operations

[atsushieno]

There are some "primitive operations" that make syntax hackily done but prevents live playing (kind of). Namely __ON_MIDI_NOTE_OFF that supports chord for 0-length notes, and __SYNC_NOFF_WITH_NEXT that supports chord for contiguous notes (arpeggio, used by "&").

They had better be reimplemented by other means.