reboot: Remove the unreachable panic after do_exit in reboot(2)

Link: https://lkml.kernel.org/r/20211020174406.17889-3-ebiederm@xmission.comSigned-off-by: Eric W. Biederman <ebiederm@xmission.com>

kernel/reboot.c

@@ -359,7 +359,6 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
 	case LINUX_REBOOT_CMD_HALT:
 		kernel_halt();
 		do_exit(0);
-		panic("cannot halt");
 
 	case LINUX_REBOOT_CMD_POWER_OFF:
 		kernel_power_off();