kill stray kernel_thread() garbage

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/parisc/include/asm/processor.h

@@ -326,7 +326,6 @@ struct mm_struct;
 
 /* Free all resources held by a thread. */
 extern void release_thread(struct task_struct *);
-extern int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags);
 
 extern void map_hpux_gateway_page(struct task_struct *tsk, struct mm_struct *mm);