Fix Planck Steno layout with new error message (remove MIDI).

keyboards/planck/keymaps/steno/Makefile

@@ -5,3 +5,4 @@ endif
 MOUSEKEY_ENABLE = no        # Mouse keys(+4700)
 STENO_ENABLE = yes          # Additional protocols for Stenography(+1700), requires VIRTSER
 AUDIO_ENABLE = no           # Audio output on port C6
+MIDI_ENABLE = no            # MIDI controls