Remove reference to timer_exit() from kernel-locking.tmpl, fix typo.

@@ -1055,10 +1055,8 @@
       Another common problem is deleting timers which restart
       themselves (by calling <function>add_timer()</function> at the end 
       of their timer function).  Because this is a fairly common case 
-      which is prone to races, you can put a call to
-      <function>timer_exit()</function> at the very end of your timer function,
-      and user <function>del_timer_sync()</function> 
-      (<filename class=headerfile>include/linux/timer.h</filename>)
+      which is prone to races, you should use <function>del_timer_sync()</function> 
+      (<filename class=headerfile>include/linux/timer.h</filename>) 
       to handle this case.  It returns the number of times the timer 
       had to be deleted before we finally stopped it from adding itself back 
       in.