sound/oss: Remove dead CONFIG_SOFTOSS*

CONFIG_SOFTOSS* doesn't exist in Kconfig or somewhere
else, therefore removing all references for it from the source code.

Signed-off-by: Christian Dietrich <qy03fugy@stud.informatik.uni-erlangen.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>