Remove dsp_has_midi_*() in favor of dsp_ioconfig()

_has_midi_*put members of LuaProc will be set according to the actual
configuration chosen, for configure_io() and run() to use.

scripts/midimon.lua

@@ -13,12 +13,9 @@ local evlen = 3
 local hpadding, vpadding = 4, 2
 
 function dsp_ioconfig ()
-	return { { audio_in = -1, audio_out = -1}, }
+	return { { midi_in = 1, midi_out = 1, audio_in = -1, audio_out = -1}, }
 end
 
-function dsp_has_midi_input () return true end
-function dsp_has_midi_output () return true end
-
 function dsp_params ()
 	return
 	{