[lab6] temp: remove enable_interrupt() in interrupt_handler()

Just to avoid instruction page fault

os/lab6/kernel/trap.c

@@ -104,7 +104,7 @@ struct trapframe* interrupt_handler(struct trapframe* tf)
     case IRQ_U_TIMER:
     case IRQ_S_TIMER:
         clock_set_next_event();
-        enable_interrupt(); /* 允许嵌套中断 */
+        // enable_interrupt(); /* 允许嵌套中断 */
         if (trap_in_kernel(tf)) {
             ++current->cstime;
         } else {