delete line 27 in clock.c, function rt_timer_switch() not used in clock.c

line 27 extern void rt_timer_switch(void);

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1857 bbd45198-f89e-11dd-88c7-29a3b14d5316

src/clock.c

@@ -24,7 +24,6 @@
 static rt_tick_t rt_tick;
 
 extern void rt_timer_check(void);
-extern void rt_timer_switch(void);
 
 /**
  * This function will init system tick and set it to zero.