How can I remove those little white line notes?

[proper]

they make the song sound like you are bashing a piano.

[trapbeat349]

Im not sure i understand what you mean, but I think you may be talking about the thin lines, you can right click them to delete them.

[♩♪♫♪♬♩♩]

just select them and then press delete, my advice, dont import midi files all as piano, in fact, dont import midi files at all