How to stop loading Xen 4.9-amd64 on boot
It should be possible to remove Xen and its related packages with a simple:
sudo apt purge xen*
As for the /etc/network/interfaces file, that looks to be pretty standard for a machine with one network connection and using DHCP. If you have configurations in your interfaces.d directory, then you may need to add this to the the top of the file:
source /etc/network/interfaces.d/*