logs spammed about missing ttyS2 device on Up^2

On Up^2, the journal is spammed every 30-60 seconds with these messages:

Jul 25 23:37:05 intel-corei7-64 systemd[1]: serial-getty@ttyS2.service: Service has no hold-off time (RestartSec=0), scheduling restart.
Jul 25 23:37:06 intel-corei7-64 systemd[1]: serial-getty@ttyS2.service: Scheduled restart job, restart counter is at 1.
Jul 25 23:37:06 intel-corei7-64 systemd[1]: Stopped Serial Getty on ttyS2.
Jul 25 23:37:06 intel-corei7-64 systemd[1]: Started Serial Getty on ttyS2.
Jul 25 23:37:06 intel-corei7-64 agetty[1174]: /dev/ttyS2: not a tty

This is due to there not being a ttyS2 device on Up^2.  Looking in the tree, this seems to be an artifact of the intel-corei7-64 machine definition in meta-intel explicitly listing ttyS2 in SERIAL_CONSOLES.  Since having more than two serial devices is uncommon on x86 platforms, I propose tweaking this the intel-corei7-64 machine template in AGL to remove ttyS2.