fix #41326: correct transposition of MIDI input

Some back and forth on this bit of code over the past few months, but I've checked and tested and the following seems to be correct in all cases (transposing non-stransposing instrument; concert pitch on / off, tested playback and toggling concert pitch button after note entry.  it also has the advantage of also being simpler than anything else we've done here (setNval does the real work later).  I like fixing bugs by deleting code!