add a "double note deleter"

[ma_spaghett]

so it deletes the note that is stacked in one block, and it left only 1 note in the block. I added this suggestion because everytime i import a midi file, there is always a specific note that is stacked / doubled.

[bentoonie]

i was thinkin about that too, it would be helpful for updating old sequences that have note stacking