remove unused member of MidiStateTracker

We store "have program" as the 8 (MSb) bit of the program
array, and similary for other state holding elements

libs/ardour/ardour/midi_state_tracker.h

@@ -85,7 +85,6 @@ class LIBARDOUR_API MidiStateTracker : public MidiNoteTracker
 	void flush (MidiBuffer&, samplepos_t);
 
   private:
-	uint8_t  have_program[16];
 	uint8_t  program[16];
 	uint16_t bender[16];
 	uint16_t pressure[16];