[kernel] Consolodate koid and close syscalls

A number of object types had _close or _koid syscalls. Moved those to be
generic for kobject.

src/kernel/syscalls/thread.cpp

@@ -7,16 +7,6 @@
 
 namespace syscalls {
 
-j6_status_t
-thread_koid(j6_koid_t *koid)
-{
-	if (koid == nullptr)
-		return j6_err_invalid_arg;
-
-	*koid =  thread::current().koid();
-	return j6_status_ok;
-}
-
 j6_status_t
 thread_create(void *rip, j6_handle_t *handle)
 {