staging: line6: drop MIDI from CONFIG_LINE6_USB_DUMP_ANY

CONFIG_LINE6_USB_DUMP_MIDI is no longer used by the code and therefore
no longer plays a role in CONFIG_LINE6_USB_DUMP_ANY.

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