staging: line6: drop MIDI dumping code

ALSA amidi(1) and aseqdump(1) can be used to dump MIDI instead of
manually dumping MIDI messages in the driver.  The advantage of using
these existing tools is that can be used at run-time rather than
compile-time.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>