kernel & libroot: Drop wait_for_thread syscall in favor of wait_for_thread_etc.

We don't have many etc and non-etc syscall pairs in this file
(the semaphores seem to be a notable exception), so drop
wait_for_thread and just call wait_for_thread_etc instead.

This breaks syscall ABI, but we've already broken it since beta5
anyway.

headers/private/system/syscalls.h

@@ -173,8 +173,6 @@ extern void			_kern_exit_thread(status_t returnValue);
 extern status_t		_kern_cancel_thread(thread_id threadID,
 						void (*cancelFunction)(int));
 extern void			_kern_thread_yield(void);
-extern status_t		_kern_wait_for_thread(thread_id thread,
-						status_t *_returnCode);
 extern status_t		_kern_wait_for_thread_etc(thread_id thread, uint32 flags,
 						bigtime_t timeout, status_t *_returnCode);
 extern bool			_kern_has_data(thread_id thread);

src/system/kernel/thread.cpp

@@ -3717,26 +3717,6 @@ _user_find_thread(const char *userName)
 }
 
 
-status_t
-_user_wait_for_thread(thread_id id, status_t *userReturnCode)
-{
-	status_t returnCode;
-	status_t status;
-
-	if (userReturnCode != NULL && !IS_USER_ADDRESS(userReturnCode))
-		return B_BAD_ADDRESS;
-
-	status = wait_for_thread_etc(id, B_CAN_INTERRUPT, 0, &returnCode);
-
-	if (status == B_OK && userReturnCode != NULL
-		&& user_memcpy(userReturnCode, &returnCode, sizeof(status_t)) < B_OK) {
-		return B_BAD_ADDRESS;
-	}
-
-	return syscall_restart_handle_post(status);
-}
-
-
 status_t
 _user_wait_for_thread_etc(thread_id id, uint32 flags, bigtime_t timeout, status_t *userReturnCode)
 {

src/system/libroot/os/thread.c

@@ -179,7 +179,7 @@ exit_thread(status_t status)
 status_t
 wait_for_thread(thread_id thread, status_t *_returnCode)
 {
-	return _kern_wait_for_thread(thread, _returnCode);
+	return _kern_wait_for_thread_etc(thread, 0, 0, _returnCode);
 }