Delete unused header file linux/awe_voice.h

Delete the unused header file include/linux/awe_voice.h, as well as
its corresponding Kbuild entry.

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>