Bootloader protocol optimization: Remove UPD_SEND_DATA's first byte ramLocation

[dallmair]

The data is transmitted over a point-to-point connection where in-order delivery is guaranteed by the Transport Layer. Also, the PC Updater tool sends all bytes over the wire, so there are no "holes" between the transmissions. Therefore, the first byte of every UPD_SEND_DATA message called ramLocation could simply be left out. Consequently, the Bootloader must then use its bytesReceived member to store the received bytes in the correct buffer location.

With Standard Frames, this should get us from ~120B/s to ~130B/s as it reduces the number of necessary UPD_SEND_DATA messages per page from 22 to 20.