Hello, Yiguang!

If I'm not mistaken, 1st "Booting from DVD/CD..." is generated by SeaBIOS: 

https://github.com/coreboot/seabios/blob/58a44be024f69d2e4d2b58553529230abdd3935e/src/boot.c#L922 

But 2nd "Press any key to boot from CD or DVD..." is shown by loader from CD. 

If other CDs boot without waiting for keypress, it's not SeaBIOS. 

That is, you'll need to tune the loader on CD itself to remove the message. 

Best regards, 

Valentine.