net: remove sockbuf::test_fn()

This was used to ensure all socket-using code was converted to C++, but not
cleaned up later.

Clean it up now.

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>

bsd/sys/sys/sockbuf.h

@@ -80,7 +80,6 @@ struct	xsockbuf {
  * Variables for socket buffering.
  */
 struct	sockbuf {
-        int test_fn();
 	struct	mtx sb_mtx;	/* sockbuf lock */
 	struct	rwlock sb_rwlock;	/* prevent I/O interlacing */
 	short	sb_state;	/* (c/d) socket state on sockbuf */