ALSA: rawmidi: remove undefined functions.

'snd_rawmidi_transmit_reset()' and 'snd_rawmidi_receive_reset()' are declared
but not defined.

This state has been continue over 10 years. So let us remove them.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>