I just wondered why two agetty processes (tty1 + ttyMFD2) were running all the time.
I believe, that the one connected to ttyMFD2 is enough. Example:
root@edison:~# ps | grep getty
218 root 2192 S /sbin/agetty -8 --keep-baud ttyMFD2 115200 xterm
220 root 2192 S /sbin/agetty --noclear tty1 linux
278 root 2420 S grep getty
root@edison:~# systemctl stop getty@tty1.service
root@edison:~# ps | grep getty
218 root 2192 S /sbin/agetty -8 --keep-baud ttyMFD2 115200 xterm
284 root 2420 S grep getty
Then I am still able to log in over the USB serial (ttyMFD2).
Hence I think that the tty1 process can safely be removed, since in the Edison configuration is it useless - there are no Ctrl+Alt+F<x> virtual terminals.