devices/midi: remove dev specific code
devices/midi: remove dev specific code

This commit removes device-specific defines from the generic
MIDI backend. These values are ignored anyway, so this should
not impact the operation in any way.

Re PR #57, thanks @simonvanderveldt for the review!

Signed-off-by: Harry van Haaren <6e1296516ee88185cd60d9725251227ece1af74d@gmail.com>

openAVproductions/openAV-Ctlra