Disable backlighting on keyboard by default

Since there's no backlighting on the SHARP display, why enable the keyboard backlighting? It's not like you can use the device in the dark. 

I think you should comment that out in the default firmware: https://github.com/sqfmi/i2c_puppet/blob/3010ada26a19612a54fb7e8258af5c5e1b93fffb/app/main.c#L36

